DOOM 3 is a single-player and multiplayer horror first-person shooter game.

Set on Mars in 2145, the story follows a newly arrived Marine assigned to a Union Aerospace Corporation research base. Routine security work is interrupted by an experiment that opens a gateway, unleashing creatures and turning personnel into zombies. With communications failing and sections of the complex locked down, the Marine is tasked with restoring systems, locating survivors, and tracing the source of the outbreak deeper into the facility and beyond.

The campaign emphasizes close-quarters tension and methodical movement. Combat mixes firearm aim with careful use of light and shadow, since many areas are unlit and enemy ambushes are common. The Marine carries conventional weapons such as the pistol, shotgun, machine gun, chaingun, and grenades, along with more advanced tools like the plasma gun, rocket launcher, and the experimental BFG. Enemies include armed zombies, fast-moving imps that throw fireballs, wraiths that blink across short distances, and heavier demons that soak up ammunition, each encouraging different tactics.

Light management is a core mechanic. The flashlight illuminates dark spaces and reveals hidden items or threats, but it occupies a hand, so the player must switch between light and weapon. Many fights hinge on listening for audio cues and reading enemy silhouettes, then choosing when to engage or retreat. Health packs and armor shards are found in the environment, and ammunition is limited early on, which pushes the player to search storage rooms, corpses, and maintenance alcoves.

Progression is structured around sector-by-sector exploration with frequent objectives delivered through the in-game PDA. The PDA stores emails, audio logs, and video clips recovered from staff, which provide door codes, storage access, and background information that unlocks new routes. Security terminals, maintenance panels, and laboratory interfaces are interactive, letting the player open lockers, reroute power, call elevators, and activate machinery to clear hazards or create new paths. Boss encounters punctuate major areas and introduce mechanics that test recently acquired weapons or environmental controls.

Navigation is aided by a 3D map and signage within the base. Save-anywhere functionality allows players to set their own checkpoints. Difficulty settings adjust enemy toughness, damage, and resource availability, changing the pace from cautious survival to more aggressive gunplay. Hidden collectibles and optional storage caches reward thorough searching.

Multiplayer supports several competitive modes, including Deathmatch, Team Deathmatch, Last Man Standing, and Tournament. Matches are designed for small player counts, with tight arenas, quick weapon pickups, and rapid respawn timers that keep momentum high. Network options include hosting, joining, and viewing server lists, along with basic customization such as frag limits and time limits.