Doom

The Union Aerospace Corporation has been experimenting with teleportation technology on Mars' moons Phobos and Deimos. After early successes, something goes wrong. It seems the scientists have opened a gateway straight to Hell. Phobos base is overrun with demonic creatures, and the whole of Deimos simply vanishes. A squad of marines is sent to Phobos, but all except one are quickly slaughtered. It falls to the surviving marine to grab some guns and strike back at the demons.

The basic objective in each level is simply to reach the exit. Since dozens of enemies stand in the way, the only way to get there is by killing them. Switches and buttons must be pressed to advance at certain points and often color-coded locked doors will block the way - matching keycards or skull keys must be found to pass.

Stylistically, the levels begin with a futuristic theme in the military base on Phobos and gradually change to a hellish environment, complete with satanic symbols (pentagrams, upside-down-crosses, and portraits of horned demons), hung-up mutilated corpses, and the distorted faces of the damned.

The game drops some of Wolfenstein's arcade-inspired aspects, so there are no extra lives or treasures to be collected for points, but many other power-ups are still available. Medpacks heal damage while armor protects from receiving it in the first place. Backpacks allow more ammunition to be carried, a computer map reveals the whole layout of the level on the automap (including any secret areas), light amplification visors illuminate dark areas and radiation suits allow travel over waste without taking damage. Also available are berserk packs (which radically increase the damage inflicted by the fists) as well as short-time invisibility and invulnerability power-ups.

The enemies to be destroyed include former humans corrupted during the invasion, plus demons in all shapes and sizes: fireball-throwing imps, floating skulls, pink-skinned demons with powerful bite attacks, and large one-eyed flying monstrosities called Cacodemons. Each episode ends with a boss battle against one or two, particularly powerful creatures.

The 3DO and Sega32x ports lack any multiplayer modes, though the other ports retain the DOS versions multiplayer to varying degrees. The SNES and Gameboy Advance versions of the game actually use different engines and hence feature numerous small gameplay differences.