Half life opposing force

Deep in the bowels of the Black Mesa Federal Research Facility, a decommissioned missile base, a top-secret experiment goes terribly wrong. As aliens come through the walls and a military death squad shoots everything in sight, young research associate Gordon Freeman must scramble to stay alive. Find your way through the monster-ridden areas of Black Mesa using your wits, limited security clearance, and a variety of weapons, ranging from a crowbar and pistols to a rocket launcher and grenades.