The game is designed to be played with 2 to 4 players, taking turns until one wins. One player takes the role of the aliens, controlling all the aliens and monsters on the Space Hulk, which were a mixture of Chaos, Orks, Genestealers and other xenos from Warhammer 40,000. The alien player takes on a significantly reduced role compared with that of a Game Master in traditional role-playing games, with his sole role being to stop the Space Marine players from accomplishing their missions.