 In Half-Life, you play as Gordon Freeman. Freeman has just began his career in the Anomalous Materials division at the enormous, underground Black Mesa Research Facility in New Mexico. Coincidentally, the facility gains control of a mysterious alien artifact, and open an interdimensional rift with an alien world, throwing the facility into disarray. Freeman must call for military aid, but in the process ends up summoning the US marines...and they dont want to just kill aliens, they want to kill all the personnel associated with Black Mesa! He is forced to shoot, smash and climb his way through ruined labs, abandoned missile silos, and vast surface areas to escape from the military, and Black Mesa!