It was a sequel to Quake II by Raven Software, using id Tech 4 (DOOM 3), notable for having a first-person cutscene in which you are "stroggified", transformed into one of the mechanical zombie soldiers you've been fighting against all game (but your NPC teammates save you at the last second before the brain implant that removes your free will is implanted). Apparently at the time, this was talked about lots in the marketing leading up to release, but when I played it as a kid, I never knew anything about that, so it was a real shock when I got to that part.

One cool thing the game did was they used the DOOM 3 "interactive panels" tech to make not only English-language human-manufactured "touchscreens", but also Strogg-language alien-manufactured "touchscreens", that you had to interact with to open doors and so forth. After becoming "stroggified", the glyphs on the Strogg touchscreens shift and you can now read them in English.

I went back and replayed it a few years ago and it's really pretty generic as far as shooters of that era go, but I thought Raven did a decent job given what they had to work with.