 In this First Person Shooter, you just got to activate switches and/or shoot everything that moves. The story is simple: a US Space Colonial Marine, sent in an outer-space researches installation owned by the state-participated UAC company (looks like ALIEN s Weyland-Yutani), is the only survivor of an inter-dimensional-gates experiment which caused an invasion of creatures from hell. Fighting through various levels (and various game sequels), armed with enough weapons to blow up the entire civilized world, he must close the inter-dimension gates, stop the hellish army and prevent the catastrophe to reach the planet Earth.