Doom 3



Doom 3 is a sci-fi horror first-person shooter computer game developed by id Software and published by Activision.

Set in 2145 in the UAC research center on Mars, it is a re-imagining of the original Doom, with a completely new game engine and graphics.

Doom 3 had a long development schedule dating back to 2000, with a well-received demonstration at E3 in 2002, 2003 and 2004. The game was finally released in August of 2004.

The game was developed for Windows and ported to Linux in 2004; five months later, it was also released for Mac OS X (ported by Aspyr) and Xbox (co-developed by Vicarious Visions). The Xbox version is graphically similar to (although less detailed than) the original and features an additional two-player online co-operation mode. An expansion, Doom 3: Resurrection of Evil, developed by Nerve Software and co-developed by id Software, was released on April 4, 2005. A Doom movie, loosely based on the franchise, was released roughly six months later on October 21, 2005.

Doom 3 focuses on slow methodical gameplay, as opposed to the “run and gun” feel as its predecessors. It received a positive reception for its fear inspiring atmosphere and groundbreaking graphics, but it was criticized mainly for its otherwise simplistic gameplay and clichéd horror effects.

Features
According to John Carmack, the lead graphics engine developer at id, the "tripod of features" in Doom 3 technology is:
 * Unified lighting and shadowing
 * Complex animations and scripting that show off real-time, fully dynamic per-pixel lighting and stencil shadowing.
 * GUI surfaces that add extra interactivity to the game

The key advance of the Doom 3 graphics engine is the unified lighting and shadowing. All 3D engines up to and including Quake III and Unreal Tournament had computed or rendered lightmaps during map creation, saving that information in the map data, which made the lighting extremely static. By contrast in the new Doom 3 engine, most light sources are computed on the fly. This allows lights to cast shadows even on non-static objects such as monsters or machinery, which was impossible with static lightmaps. A shortcoming of this approach is the engine's inability to render soft shadows and global illumination.

As well as dynamic lighting and shadows, the Doom 3 engine was id Software's first to make extensive use of bump mapping.

To create a more movie-like atmosphere, id interspersed the gameplay with many in-game animated sequences of monsters ambushing the player or just lurking around.

To increase the interactivity with the game-world, id designed hundreds of high-resolution animated screens for in-game computers. Rather than using a simple "use key", the crosshair acts as a mouse cursor over the screens allowing the player to use a computer in the game world. This allowed an in-game computer terminal to perform more than one function, such as a readily apparent door-unlocking button, combined with a more obscure function allowing an astute player to unlock a nearby weapons locker.

Other important features of Doom 3 engine are normal mapping and specular highlighting of textures, realistic handling of object physics, dynamic, ambient soundtrack and multi-channel sound.

id Tech 4 engine
id Tech 4 (AKA the "Doom 3 engine") began as an enhancement to id Tech 3 which was used in Quake III Arena. Originally it was planned to be a complete rewrite of the engine's renderer, while still retaining other subsystems, such as file access, and memory management. After the new renderer was functional, however, the decision was made to switch from C to the C++ programming language, necessitating a complete restructuring and rewrite of the rest of the engine; today, while the Doom 3 engine contains code from id Tech 3, much of it has had to be rewritten.

Hardware Requirements
A disadvantage of id Tech 4 was that it needed a high-end graphics processing unit (GPU), which was at least DirectX 8.0 compliant with fully programmable vertex and pixel shares, such as the Nvidia GeForce 3 or ATI Radeon 8500, with 64 MB of VRAM. By E3 2002, the recommended GPU was the Radeon 9700; while its DirectX 9.0 features are not necessary to render the game, its advanced architecture, 256-bit memory bus, and efficiency were needed to run Doom 3 at high detail and playable speed.

id Tech 4 resulted in the obsolescence of DirectX 7.0 graphics chips such as the widespread GeForce 2 and Radeon 7200, as well as DirectX 6.0 chipsets such as RIVA TNT2 and Rage 128, and software rendering (with an integrated Intel GMA). Until the advent of id Tech 4, owners of pre-DirectX 8.0 cards were able to use a powerful CPU to compensate. While John Carmack initially warned gamers not to purchase the GeForce 4 MX (which was an improved GeForce 2), its somewhat widespread adoption compelled id Software to enable Doom 3 to run on these cards, making it the only DirectX 7.0 chip capable of running Doom 3.

From 2001-2003, DirectX 8.0 capable video cards were extremely expensive, putting them out of the range of all but the most hardcore gamers. However, id Software pointed out that the original Doom and Doom II had gamers moving from their 386s to 486s, while the first Quake had them switching to Pentium processors. They hope that Doom 3 would do the same in getting the masses to adopt DirectX 8.0 hardware.

Plot


The protagonist is once again a nameless space marine. As it just so happens, he gets shipped to the UAC Mars research facility with Councilor Swann and his bodyguard Jack Campbell on the same day all Hell breaks loose. Within minutes of the invasion, the main military units are destroyed or zombified. It is once again upon the player to stop the forces of Hell from reaching Earth.

The first cut scene displays Swann saying how fed up he is to Campbell about being sent to Mars to check security. Swann says to Campbell he is “…tired of doing damage control every time [he] screws up.” Swann is later seen arguing with the head research scientist in Delta Labs, Dr. Betruger, saying there are too many incidents happening throughout the base, along with frightened employees and rumors of what is happening in Delta Labs.

The player's first mission, assigned to him by Master Sergeant Kelly, aka “Sarge”, is to find a missing scientist named Jonathan Ishii that was said to be seen at the old communications facility. When found, he babbles about sending out a warning - “The Devil is real. I know. I built his cage.” With those words, Hell erupts from the gateways, sending a shock wave through the complex, along with glowing pentagrams and scores of evil ghost skulls that transform nearly every human into zombies, including Ishii.

Changes from original Doom
Similar to the story of the original Doom, the game focuses on the marine who is transferred to Mars and sent out on a routine mission, and who needs to kill zombies and demons from Hell. The main difference is that in Doom 3, the game takes place on Mars itself, instead of Phobos and Deimos, where the first two episodes of the original Doom take place. The environment of Doom 3 is much more realistic. For example, whereas the original Doom gives the two moons breathable atmospheres, Doom 3's Martian atmosphere is unbreathable.

In both cases, the protagonist visits Hell. In the original Doom, it is the third episode Inferno (Ultimate Doom adds a fourth, Thy Flesh Consumed, which also takes place in Hell), whereas in Doom 3, it is only one level, but Doom 3's one Hell level is much longer and more intense than the others, and has a boss.

For Doom 3 id Software employed a professional science-fiction writer named Matthew J. Costello to write the script and assist in story-boarding the entire game. id Software focused on retelling the story and creating a tense horror atmosphere. The game's events and atmosphere show a great deal of influence from George Romero's Living Dead series and James Cameron's Aliens, as well as Valve Software's Half-Life.

Unlike in previous id games, there are now cut scenes that give purpose and context for the player's actions and introduction to new enemies. Similar to other science fiction action/horror games such as System Shock, System Shock 2 and Aliens versus Predator 2, hundreds of text, voice, and video messages are scattered throughout the base. The messages are internal e-mails and audio reports sent between lab workers, administrators, maintenance staff, and security personnel at the Mars base. The messages explain the background story, show the feelings and concern of the people on the Mars base and reveal information related to plot and gameplay. Video booths and televisions give planetary news, corporate propaganda, visitor information and technical data about the base.

The story of Doom 3 surrounds the discovery of ancient ruins underneath Martian soil. Tablets found at these sites record how an ancient Martian race developed a form of teleporter technology. They realized an important fact all too late, however; the route the teleporter took passed through Hell. Quickly invaded by demons, this alien race created and sacrificed themselves to a weapon known as the Soul Cube. This cube, powered by the souls of almost every being of this alien race, was used by their strongest warrior to defeat and contain the demons in Hell.

Having done so, the remainder of the alien race constructed warnings to any who visited Mars, warning them not to recreate this technology; to avoid opening another gate to Hell. They then teleported to an unknown location, fleeing Mars; there are hints that at least some of them fled to Earth, and that humans descended from them. It's stated that the demons once inhabited Earth in an unknown context, but lost possession of it due to an unknown cause. Consequently, the demons want to reclaim Earth.

Development
In June 2000, John Carmack announcing the start to a remake of Doom using next generation technology. This plan revealed controversy had been brewing within id over the decision.

Kevin Cloud and Adrian Carmack, two of id Software's owners, were always strongly opposed to remaking Doom. They thought that id was going back to the same old formulas and properties too often. However, after the warm reception of Return to Castle Wolfenstein (which was originally a remake of Wolfenstein 3D) and the latest improvements in rendering technology, most of the employees agreed that a remake was the right idea and confronted Kevin and Adrian with an ultimatum: "Allow us to remake Doom or fire us" (including John Carmack). After the reasonably painless confrontation (although artist Paul Steed, one of the instigators, was fired in retaliation), the agreement to work on Doom 3 was made.

The game was in development for 4 years. In 2001, it was first shown to the public at Macworld Conference & Expo in Tokyo during the unveiling of Nvidia's GeForce 3, with Apple CEO Steve Jobs introducing John Carmack on stage, who showed off a few new screenshots of id Tech 4, including some from the Doom 3.

It was later demonstrated at E3 in 2002 using an ATI Radeon 9700, where a 15-minute gameplay demo was shown in a small theater. It won awards at E3 that year. It starts off with Dr. Betruger (with spectacles) pushing his way past a couple security guard to initiate a test run. However, computer systems starting going haywire and evil spirits were released from a portal. One guard is possessed by the spirit and briefly lifted into the air, with his skin shriveling up and his goggles/visor exploding as he is transformed into a mindless zombie. After a brief vision of hell, the movie cuts to a nameless marine, taking the player's first-person shooter view. The player kills various zombies, imps, and commandos, before running out of ammo and being killed by a Hell Knight, who then rips off the player's head (the camera view) and eating it. One memorable scene is when a Pinky Demon is eating the intestines of a Fat Zombie in the bathroom. The movie was never released on the internet, though bootleg versions exist.

At the same time of the E3 2002 demo showing, a downloadable film made by Fountainhead Entertainment was released, called Doom III: The Legacy, which contrasted Doom/Doom II with the new Doom III and featured interviews with key id Software staff.

Some speculated that id software was targeting the 2002 holiday season, although others believed a 2003 release date would be more realistic. After E3 2002, there was no further press release from id Software regarding the project; the company's website only had Return to Castle Wolfenstein as the latest game. Late in 2002, a couple of employees at ATI Technologies leaked a development version of Doom 3 onto the Internet.

Next year, a new trailer was shown at E3 2003 and soon afterwards the id software homepage was updated to showcase Doom 3 as an upcoming project but it was also announced that Doom 3 would not be ready for the 2003 holiday season. According to some comments by John Carmack, the development took longer than expected. Originally, the game was planned for release around the same time as another highly anticipated game, Half-Life 2, in Christmas 2003. Doom 3, Half-Life 2, and Halo 2 were considered among the most anticipated games since their announcements in 2001/2002, though all three of them would not make the planned 2003 holiday season.

Doom 3 achieved gold status on July 14, 2004, and a Mac OS X release was confirmed the next day on July 15, 2004. Doom 3 was released in the U.S. on August 3, 2004. Additionally, a Linux version was released on October 4, 2004. Due to high demand, the game was made available at select outlets at midnight on the date of release. The game was released to the rest of the world on August 13, 2004 (except for Russia and other countries of the former Soviet Union, where official localization was delayed and caused the game to be released about four months later, on December 10, 2004).

Two days before its official release, Doom 3 was released by pirate groups onto the Internet. As the game's focus is its single player mode, the need for a valid retail serial number for online multiplayer gaming was a weak deterrent against piracy.

Gameplay
Doom 3’s gameplay was not as fast paced as the games before it. Most of the game is extremely dark, and there is no Light amplification visor. Instead the player must rely on a flashlight that can only be used in place of a weapon. There are few tactics involved other than grabbing the biggest weapons.

Much of the game takes place in dark close-quarters with demons ambushing from every direction. By contrast the Hell section of the game is considered by many to be the best, as it features more open areas and makes use of unique effects.

Difficulty
There are four difficulty levels in Doom 3: Recruit, Marine, Veteran, and Nightmare. The first three are always available. On Recruit difficulty, there are fewer monsters, but it is a negligible amount. The principal difference between the difficulties is the amount of damage the player receives. The chart on the right indicates the amount of damage the player will receive on each difficulty level, relative to the definition files (.def).

Upon completion of a campaign regardless of difficulty level, the player unlocks the "Nightmare" difficulty setting. When playing the game on this setting, the player's health falls in 5-point increments at 5-second intervals until it reaches 25, where it remains steady. Additionally, there are absolutely no medkits throughout the game; the only means of procuring health is either by the health stations, which are still operational, or use of the Soul Cube, which is given to the player at the very start of the game.

The difficulty setting can be controlled by the controllable variable,. The damage changes take effect immediately, but a map restart or change is necessary for the rest. For example, if a player begins the level on Recruit difficulty and then enters  in the console, immediately their health will begin its drop to 25 and they will receive Nightmare damage. However, the Soul Cube is not given, medkits remain in the level, and the amount of monsters does not increase.

Weapons
Most of Doom 3's weapons are updated versions of the classic weapons, but those marked with an asterisk are new additions to the series. Several weapons are also based upon these found in Quake 2. As the game generally takes place in dark mazes, there is no long distance "sniper" weapon such as the Railgun found in Quake 2 and 3. As in previous Quake titles, Doom 3's rocket launcher allows rocket-jumping, but it is of little or no use in closed levels.


 * Fists
 * Flashlight*
 * Pistol
 * Shotgun
 * Machine gun*
 * Chaingun
 * Plasma gun
 * Rocket launcher
 * BFG 9000
 * Chainsaw
 * Grenades*
 * Soul Cube*

Monsters
See main article: Doom 3 Monsters.

References to Classic Doom
See main article: References to Classic Doom in Doom 3.

Final Storyline
In a later cut scene, Swann is seen in a video phone conference with Betruger who is rather calm about the situation. Betruger claims the situation is under control. After deciding on whether to alert the orbital fleet, Betruger addresses you over a computer screen and says that once the fleet arrives, his legion will take the ships back to Earth, thus revealing that he commands the monsters that have overrun the base.

Later in the game, the player runs into a colleague of Betruger, who says that he became obsessed with the teleporters when he figured out Hell existed on the other side. He says he took an artifact called the Soul Cube from the archaeological digs from the ancient Martian civilization into Hell, and demons followed him out.

The player never meets up with the remaining Marines, save for one in a cutscene that dies shortly afterwards. He only reaches Swann and Campbell on their deathbeds. Swann was badly injured, and Campbell went on to hunt Sarge. Swann says that Kelly has turned evil and is now on Betruger’s side. However, Sarge mortally wounded Campbell and taken his BFG 9000. After killing Sarge, the player finds an archaeologist, who explains that the Soul Cube must be used to stop the demon invasion.

After entering the Primary Dig Site, the player discovers a section of Hell that has crept into the Martian underground and deep within the bowels of this Hellscape, they encounter the invulnerable Cyberdemon guarding a “Hell hole” — a portal to Hell. Defeating the Cyberdemon, which is only possible with the charged Soul Cube, the Cube seals the Hell hole and the game ends, leaving many questions unanswered.

Levels
Most of these maps are quite large and each typically require 1+ hours each on a player's first run through the game.


 * 1) Mars City
 * 2) Mars City Underground: Union Aerospace Subsystems
 * 3) Mars City: Union Aerospace Corporate Division
 * 4) Administration: Union Aerospace Corporate Division
 * 5) Alpha Labs - Sector 1: Union Aerospace Science Division
 * 6) Alpha Labs - Sector 2: Union Aerospace Science Division
 * 7) Alpha Labs - Sector 3: Union Aerospace Science Division
 * 8) Alpha Labs - Sector 4: Union Aerospace Science Division
 * 9) Enpro Plant: Energy Processing and Storage
 * 10) Communications Transfer: Maintenance and Transfer Station
 * 11) Communications: Central Communications Tower
 * 12) Monorail Skybridge: Facility Transport
 * 13) Recycling - Sector 2: Waste Recycling Center
 * 14) Monorail: Facility Transport
 * 15) Delta Labs - Level 1: Union Aerospace Research Division
 * 16) Delta Labs - Level 2a: Union Aerospace Research Division
 * 17) Delta Labs - Level 2b: Union Aerospace Research Division
 * 18) Delta Labs - Level 3: Union Aerospace Research Division
 * 19) Delta Labs - Level 4: Union Aerospace Research Division
 * 20) Hell
 * 21) Delta Complex: Union Aerospace Research Division
 * 22) Central Processing: Processing Distribution Center
 * 23) Central Processing: Primary Server Bank
 * 24) Site 3: Analysis Facility
 * 25) Caverns - Area 1: Excavation Transfer
 * 26) Caverns - Area 1: Artifact Excavation
 * 27) Primary Excavation: Artifact Dig

Xbox Port
The Xbox version was sold in both a standard case, as well as a special edition sold in a metal case. The metal case edition had several extras—interviews, G4’s Icons Doom episode, early artwork, and the full versions of Ultimate Doom and Doom II. The Xbox Collectors edition includes two more levels, one in Ultimate Doom (E1M10: Sewers) and one in Doom II (MAP33: Betray).

The Xbox port's textures are less detailed than that of the PC version and splits many levels up into separate parts due to console limitations. Nonetheless, most reviewers were impressed that the Xbox had otherwise retailed all of the other features, considering that its NV2A graphics processor (equivalent to an Nvidia GeForce 3, the original base card for Doom 3) was a generation behind the recommended video cards (ATI Radeon 9700 and GeForce 4 Ti) for the PC version. The NV2A processor was what distinguished the Xbox from the PlayStation 2 and GameCube, the latter two consoles were not considered for a Doom 3 port due to insufficient hardware. The PC version had been originally designed with the GeForce 3 in mind but now that GPU is barely sufficient to run the game; a Radeon 9700 was used to run the E3 2002 demo.

The Xbox version has added co-op play, which required the modification of levels, such as widening corridors to comfortably accommodate a second player.

This version is compatible with Xbox 360.

Xbox Controls
Left Thumbstick: Move

Right Thumbstick: Look

Click & Hold Left Thumbstick: Crouch

Click & Hold Right Thumbstick: Zoom

A: Jump

B: Previous Weapon

X: Reload

Y: Next Weapon

Left Trigger: Sprint

Right Trigger: Action

White (LB for 360): Equip/Unequip Flashlight

Black (RB for 360): PDA/Multiplayer Score

Start: Pause

Back: Save/Ready

The D-Pad arrows serve as hotkeys to select weapons instead of cycling through every weapon in inventory. Four weapons can be assigned. The weapon assigned to each arrow is customizable.

Reception
Few games have polarized gaming as much as Doom 3 has, and many reactions to the game are in heavy contrast to one another.

Criticism
Some commonly named shortcomings of the game are:


 * Reliance on traditionally overused horror techniques such as pitch black darkness, limited use of the flashlight and stock horror movie clichés, which may make the game frustrating to play rather than scary or atmospheric[4]
 * Repetitive gameplay, similar linear levels during parts of the game[5][6]
 * Slow movement unlike the faster play speed of Doom, Doom 2 and the Quake series
 * Unlike contemporary first-person shooters, movement is simple; the player can move, jump, crouch and sprint, but can't go prone or lean around corners.
 * No ability to use the flashlight and the weapon at the same time (known as "No duct tape on Mars" problem, whereas today many real-life weapons have hands-free light attachments (however, many light-mods on the internet add a flashlight to the guns)
 * Somewhat stale storytelling techniques, forcing the player to read or listen to messages by hiding access codes in them, and a shortage of cut-scenes providing story exposition, with one reviewer saying that adding clumsy storytelling to the game ending up weakened the experience
 * Poor monster AI, over-reliance on scripted sequences. Particularly with monster ambushes that are triggered by the player, while some do fit in with the premises of the level (demonic enemies can be reasoned to come from flaming vats), other enemy spawn points are simply at where powerups are.
 * Somewhat limited use of physics (improved significantly in the expansion)
 * All weapons are direct-fire, point-and-shoot weapons with no alternate firing modes without any variation or innovation.
 * Slow ammo reload times that too often caused ranged fights to become blind button-mashing melees
 * The shotgun is absurdly inaccurate, forcing the player to fire at point-blank range in order to hit the target with all of the pellets and ensure a one-shot kill.
 * A small multiplayer deathmatch mode of only a few people, stemming from Doom 3's focus on the single player experience.
 * No official cooperative gameplay in the PC version whereas the original Doom contained a cooperative mode.

Some critical reviewers consider that the technological level of Doom 3 is similar to that of other games of 2004, and that features such as bump mapping had already become industry standard.[citation needed] For example, an often mentioned feature of Doom 3, per-pixel lighting and stencil shadowing, had already been implemented in many games released in 2003, even a budget title from Activision Value called Secret Service: Security Breach.

Rebuttals to criticism
Many gamers argue the apparent shortcomings are not shortcomings at all, but are integral to the gameplay id determined to display for Doom 3.

Since Doom 3 is a remake of the original Doom - a game which did not have high-end concepts common in today's more complex games - remaking Doom with too much complexity would remove a key component that made Doom popular in the first place.

The deliberate slow pace, horror clichés, and overly scripted sequences (including the randomness of enemy spawning points) is designed to inspire terror. Every aspect of the game, from the lighting and sound to interactions and monster ambushes contribute to an overall feeling of fear and anxiety. 

The flashlight is a key element of Doom 3's gameplay: the player must balance between seeing the enemy, and defeating it. Almost every monster has glowing eyes, or some aspect of bio-luminescence which offers a target for the player. If weapons had a light attachment, this results in the mystery of "the unknown" to be less potent and frightening. Additionally, muzzle flashes can be enabled for marginally better visibility while firing.

Another rebuttal concerns the story of Doom 3, which is done through the use of audio and video logs. The use of logs in this way is similar to the use of logs in System Shock 2. Ken Levine, lead designer of System Shock 2 said of the logs in Doom 3 "It amazed me when I played Doom 3 that they didn't mix their recordings into the ambient space of the world. The people sound like they're in a recording booth."

A few of these criticisms of Doom 3 are based on expectations for other types of FPS games. During development, it was often compared with the equally anticipated Half-Life 2. Some have argued that since Doom 3 was released before Half-Life 2, many have come to expect things from it that they previously had expected from Half-Life 2. For example, the common complaint about Doom 3's lack of environment interactivity could be considered a subtle complaint that Doom 3 doesn't have a Half-Life 2-style "Gravity Gun", a weapon which can be used to throw or push many objects in the world, including small objects, cars, and organic lifeforms. Ironically, Doom 3 was said to have a "Gravity Gun" item designed long before Half-Life 2, but was not in the game proper. This weapon appears in the Doom 3 expansion known as Doom 3: Resurrection of Evil, which has drawn the ire of those who feel id is pandering to Half-Life 2 fans.

With regards to a minimal multiplayer mode, the designers intended that Doom 3 would be played and remembered primarily for its single-player story experience, as opposed to id Software's previous titles which were known far better for multiplayer deathmatch. (The follow-up Quake 4 would have a return to multiplayer focus using Doom 3's engine.) The Xbox port of Doom 3 did implement co-op mode but in order to make the co-op mode feasible and balance out gameplay, levels had to be redesigned to accommodate both players.

Sales
Despite its apparent flaws, the game was still a commercial success for id Software, with the planned total revenue estimated by Activision at $20 million. It was one of the top selling games of 2004, alongside Halo 2 for the Xbox and Half-Life 2. The financial success was bolstered by the near-record number of pre-orders placed for the game.

id Software also typically benefits from licensing the engine to other developers. Several games have already been developed using a modified Doom 3 engine, including Quake 4, Enemy Territory: Quake Wars, Castle Wolfenstein (tentative title) and Prey.

As of August 23, 2006 Doom 3 has garnered an average review score of 87%, according to 97 media outlets on GameRankings.com. By the same source, it is in the top 10 PC games of 2004.

E3 2002 Game Critics Awards: Best of Show, Best PC Game, Best Action Game, Special Commendation for Sound, Special Commendation for Graphics.

Trivia

 * The Doom community long predicted a sequel to Doom II, usually referring to it as Doom 2000. Some speculation is recorded in this Doomworld mailbag from 1998-08-18.
 * TimeSplitters: Future Perfect parodied the Doom 3 audio logs in the level What Lies Below. In this level, Cortez can access a scientists’ personal audio log, which contains his locker code (or, at the very least, several three-digit numbers which he believes are his locker combination).
 * The character of Dr. Reinhard in Evil Dead: Regeneration may be a parody of Dr. Betruger. Both share a similar physical appearance, including a solid white eye. Both men also started out good but turned evil when tempted by the forces of Hell.
 * A terminal after returning to Mars from Hell displays a red screen. An email can be downloaded from this terminal, containing a rather tongue-in-cheek message written by the Hell demons on proper human sacrifice techniques.
 * In the final room before the Cyberdemon encounter, a small Id Software logo can be found on one of the bricks in a corner. Approaching this turns the crosshair into a mouse arrow as would happen if the player approached a terminal. Clicking this opens a secret room which contains a PDA. Picking this PDA up downloads special "thank you" messages from the iD software staff.
 * The large Hell Gate that is present on the menu selection screen resembles the Stargate from the movie/television Stargate franchise, with the constellation markings replaced by runes.
 * The name 'Dr. Betruger' has a strong similarity to the German word 'Betrüger' which means 'traitor'.

Mods

 * The Classic Doom for Doom 3 mod replays Knee-Deep in the Dead but with the new Doom 3 engine.
 * The Last Man Standing mod enables cooperative play, and introduces a new game type.

Other mods for Doom 3 include:
 * A mod that puts lights on the weapons (but which are less effective than the flashlight)
 * A mod that prevents the bodies of the monsters you killed from disappearing
 * A mod that makes the Cyberdemon at the end of the game vulnerable to weapons other than the Soul Cube
 * A mod that makes the game much easier to beat if having a hard time

A mod featuring the Doom 3 weapons for Classic Doom source port ZDoom also exists. It includes several Doom 3 weapons (using sprite-based graphics and Decorate to recreate the weapon behavior) except for the grenades and Soul Cube. The mod works with both Doom and Doom II, though the mod lacks the super shotgun when played with Doom II.

Expansion
See Doom 3: Resurrection of Evil