An unnamed space marine takes on monsters and demons on the moons of Mars in this port of the blockbuster PC first-person shooter. Players must travel the mostly dim and often scary assemblage of rooms, hallways, stairwells, caverns, mazes, and more to reach the exit and move on to the next stage. Of course, a horde of possessed marines, imps, demons, and other hellish monstrosities stands in the way.