I had the same experience with AVP2. The sound of those bastard xenomorphs breathings
.. ticking ... their light footsteps .. I've never been scared in a game like that before, never. You don't even see a single alien for the first 20 minutes of the game, and but you see the proof that they've been around and you can hear them. By the time you finally see one, you've been dreading the moment for so long you practically douse yourself.