All of the They Hunger mods for Half Life were fucking masterpieces. FEAR has some awesome moments, and the last 15 minutes or so are pants-shittingly tense.

Bioshock has some damn goodmoments, especially the room in the Medical Pavilion that fills with fog, then slowly clears. there is a gene tonic on a cabinet, and when you go to retrieve it, you turn around, and a psychotic splicer Doctor is right behind you.

I remember that splicer doctor.Played the game twice and even though I was expecting it the second time it still made me jump.