F.E.A.R. and Doom 3 are the scariest games I've ever played. F.E.A.R. actually scared me so bad I had to stop playing for a while before I picked it up again. I had come across four bloody skeletons in a massive pool of blood in some office building atrium, and when I just randomly looked up in the corner, little Alma flashed into existence with a blood chilling scream literally ten feet away from me! I was already on pins and needles, and that one just pushed me over the edge. I quit before even bothering to save my game. And when I got back to that same point the next day and looked up to the same corner, she was nowhere to be found...
And Doom 3 was just a bloody boo-scare nightmare. The atmosphere of that game was just crazy intense! I don't care if I have the BFG 9000 in my inventory, I'm walkin' around with my flashlight out so those jerks don't sneak up on me again!