WAY ahead of it's time.
This game not only inspired mods for the many FPS games that came out afterward, it inspired an entire genre. How can you possibly top that? This title deserves to be mentioned in the same breathe as Doom and Final Fantasy. Perhaps even before as the other two mentioned didn't spawn a genre, but merely solidified them.
The use of speech in this game was something also rarely done at the time. What's amazing is that it did them so well. The voice acting was well excuted, and done in such a believable way that you come away with an experience that you probably never will forget.