A lot of people think Wolfenstein 3D were the first 3D FPS game. Ultima Underworld was released have a year prior. It had non-orthogonal geometry (walls/floors/ceilings at various angles, not just 90°). It had rivers with current in which you could swim, basic physics, a faction system for the NPCs, auto-mapping... the list goes on and on. This was the most ahead-of-its-time game I have ever played in 40 years as a gamer. It was also the inspiration to the Elder Scrolls series. And it was a damn good role playing game in its own right! The only downside was that the CPU demands were pretty high for its time so a lot of people couldn't really play it.
This game is a major milestone in gaming history that influenced all FPS games that came after. As such, I believe it is worth being preserved.