Slender is a first-person survival horror game made by Parsec Productions, a one-man studio lead by Mark J. Hadley. You take control of one man/woman, with only a flashlight, as you explore a small forest looking for 8 sheets of paper while being stalked by what is known as the
Slender Man.
The more sheets you collect, the closer the Slender Man gets, and the more dramatic the music becomes.
http://www.parsecproductions.net/slender/
It's quite creepy, and the atmosphere is terrific, at least in my opinion. Other then that..

I'd recommend checking it out if you get the time..
It is not a very hardware-intensive game, but the simplest machines will have trouble running it even at the lowest settings, so try to have at least some kind of hardware acceleration.