Watch Toby Turner's videos, you'll roflyao :rofl:
Actually I think it's better to play the game without having seen videos of it.

I bought Amnesia when it was on sale recently but haven't had time to install it yet.
Is it really and truly scary?
The thing is that it gets the horror genre right. It doesn't throw the enemy straight in your face all the time, or gives you the weapons to deal with them. Instead, you barely ever get a good sight of them, encounters are fairly rare, but you never stop feeling like there's something around. But nothing jumps out most of the time, so the tension stays. Psychological horrorz!
Amnesia: The Dark Descent and System Shock 2 for me. System Shock 2 is great at keeping the tension going because none of its menus pause the game, enemies respawn to some rate, so you never feel safe. And there's limited ammo around. Penumbra and Call of Cthulhu DCotE are good too.