Doom 3 Online is a first-person shooter presented with early 3D graphics. The player controls an unnamed space marine through a series of levels set in military bases on the moons of Mars and in Hell. To finish a level, the player must traverse through the area to reach a marked exit room. Levels are grouped together into named episodes, with the final level focusing on a boss fight with a, particularly difficult enemy. Enemies often appear in large groups, and the game features five difficulty levels which increase the quantity and damage done by enemies, with enemies respawning upon death and moving faster than normal on the hardest difficulty setting.

How to play: Use arrow keys to control the character move and click to fire.