On June 22nd, 1996, id Software released Quake, the true successor to the Doom franchise and among the first games (certainly the most well-known) to be presented entirely in 3D. That is, with polygons. Those of us old enough to do so will remember the first set of levels (that is to say, the demo) with perfect clarity, and recall the classic grunts, moans, and clangs that accompanied that fantastic atmosphere and ambitious level design.
It’s still a hell of a lot of fun. You can download a version compatible with modern Windows and OS X here, and there are tons of mods and level packs at Planet Quake. Graaaa!