A modern remake of the Quake II mod Gloom. IIRC, but the internet seems to have forgotten it, it used to be called Aliens vs. Marines before it got FOX'd. Might even have been the origin of that term. Not sure. Asymmetric class-based FPS with evolution/progression elements. Similar idea to Natural Selection, but quite different in practice.

There was a similar game called Tremulous much later, but I never ended up playing that.