Really? NO ONE has mentioned the STALKER series? Has anyone on the Escapist even played those games? Cause I'd be sorely dissappointed in this place as a gaming community if they hadn't.
Seriously, next to Condemned, STALKER is the only game that has seriously freaked me out. Namely the part in Shadow of Chernobyll called "The Brain Scorcher". You have to go into a derelict bunker filled with mutants to turn off a device that has been frying peoples brains and turning them into zombies.
First, as you near the bunker, the screen goes sepia and staticy, and you begin to hear Russian radio transmissions whispered around your head. Then ghostly "echoes" of mutated animals start to assault you, but they disspate if you shoot them or when they touch you. Then when you actually get into the base, it's pitch black, filled with deadly anomalies that can kill you in an instant, and there's eerie noises from every direction. "Snorks", degenerated humans wearing gas masks, run on all fours and lunge at you. And worst of all, a creature with telekinectic powers can pick up objects and fling them at you any time, meaning every item is a potential danger.
20 minutes crawling through that situation, and your nerves are shot. Best scary/tense scene I've ever played in a game. I both dread and look forward to it every time I play.