Alien/s and Predator(!=2) are legendary Sci-Fi. In fact, thinking about it now, it makes me sad that Sci-Fi hasn't come close to being that good in so long.
I think AvP is a highly under rated FPS. It caught the atmosphere really well and the motion sensor for the marine was quality. The first truly scarey FPS in my opinion. Bleep bleep - bleep bleep - bleep bleep - then the scream of the alien and it running along the ceiling. WAghhgggggggggggggggghhhhhhhhhhhh!!!
And don't forget, you got 3 games in 1! Playing the Alien is still the most unique FPS action experience I've played. I really got the hang of skuttling up walls and hanging on the ceiling, waiting for marines to walk underneath then dropping down and chopping them up. Ultimate sneekage and quality 180 degree panoramic FoV. You really felt like the Alien.
And the predator ... the whole arsenal! Invisibility on tap, shoulder mounted auto aiming canon. Still a challenge, but you felt well hard! Just auto aiming on people and blowing them away, and switching your vision mode to infra-red to see heat sources etc.
Anyways! A great old game, and I look forward to these new games hopefully being as innovative. I have a fear they wont be, but just maybe they'll do it justice.