Half-Life

(Jesus there's a lotta people who credit the devs of this game for inventing things they absolutely did not invent or convergently evolved in multiple games.)

A game of two halves pretty much at each other's throats. In one corner, the sleek, scripted tour of Hollywood cinematic setpieces. In the other, the mean little sequence of paranoia-inducing gotchas designed to kill you at least once, if not multiple times—tanky hitscanners, janky physics, explosives everywhere—in the spirit of the worst “rocks fall, everyone dies” dungeon master stereotype imaginable. Spielberg and the DM hate each other. They will kill each other. And we all have to suffer the consequences.

Also it has maybe the worst-feeling shotgun of any 90s FPS. Awfully powerful sound for all the force of a dry fart.