Amnesia: The Dark Descent, a first person survival horror. A game about immersion, discovery and living through a nightmare. An experience that will chill you to the core.
I played this not long after it was released but never remembered to rate.
This game is without a doubt one of the best games I have ever played, it's now 2013 and it's at the top of my recommendations list. It's a far bigger game than being scared all the time; it's so profound in terms of story telling and understanding the position of your character. It's deeply disturbing (in a good way), as you're making your way down dark corridors, wondering what is beyond the door you're about to open, whimpering as you turn a corner.
If you have not played this yet (unlikely), and you're thinking about playing it, do yourself a favor; play it, read every note you pick up, look at every picture you find, and most of all: have fun!
Incredibly tense and scary game; the lack of combat makes it stand apart from the crowd, although it's not the first horror game to do something like that. It is the first horror game to make me scream out loud, though, so that has to count for something.