AvP? Atmosphere? No. That has cheap slasher movie thrills. "Oh an alien! Oh a predator! Oh, i fear!" BAH, I say.
System Shock 2 makes you FEAR. It makes your belly twist and seriously reconsider going through that door. "we are we are we... are... is there another? your song is not ours.... silence the discord...." Cyber ninjas, mutated people, invisible spiders, crazy security turrets, security cameras, psychic monkeys, C3PO on crack and the voice of the Many in your head...
Thief is also good. Make one mistake and then watch them search for you, while you hide in the shadows and pray they come your way! Or when you're walking along and you see a dead body and you go over to it and.... its just a dead body but while you're looking at it, something shambled up behind you. You step away and draw steel and try to kill it and IT DOES NOT DIE. All it does is moan and keep coming and you don't have any holy water or fire arrows and all you can do is run and OH DEAR GODS THERE'S ANOTHER ONE!
Oh yeah. THAT'S atmosphere. THAT's setting. THAT's mood. AvP? Cheap schlock twitch action crap. Its Quake3 with more character, but still not a candle to Shock2 and Thief1&2.