Gotta have several but a list of what comes to mind on a short notice:
1. Wing Commander - "The Game", this one made PC gaming serious contender over Amiga. Also, pretty mindblowing in that date.
2. Ultima VII (Parts I and II) - Dynamic environs instead of sprites shaded in situ, good storyline. Even today, still one of the best CRPG's ever made.
3. Ultima Underworld - How far ahead of iD (and other non-cerebral shmups) Origin/looking Glass was at this time, not stuck in 2,5D and bolting real RPG mechanics and story on 3D environs, instead of shoot everything that moves and then some.
4. System Shock - Another mind blowing experience back at release, maybe Origin/Looking Glass collab at it's finest.
5. Morrowind - Still maybe the best game set in Tamriel. Also, still an "real" RPG where stats, not controller skill mattered.
Several later games could have honourable mentions, as could earlier Amy/C64 titles, but not going into that rabbit hole
