Games to make me shit my pants.

Hey Giantbomb,  
I've just finished watching Hamst3r's play through of Amnesia: Dark Decent (i recommend watching its really well done), and now Im in the mood for a scary game to play with the lights off.  
However i don't really go into the horror genre much so i was wondering if you'd be able to help me out by suggesting some games for me to take a look at?  I'd like a game thats got a descent narrative too, so that i have an Incentive to continue playing. I'm open to pretty much any type of game from action horror such as dead space, to puzzle or narrative based games such as Amnesia. 
So suggest a game and i'll check it out, all help is appreciated :) 
 
Edit: should mention the game would have to be on 360 or Mac.

I shit my pants? 
 
They give you an achievement for shitting your pants. 
 
On topic - Fuck.  Doom.  3.

See how many boxes of laxatives you can eat in 10 minutes and try to break that record a hour later 

" I shit my pants?  They give you an achievement for shitting your pants.  On topic - Fuck.  Doom.  3. "

F.E.A.R. 2 and Condemned 2 were pretty good for night time, no light playing. But Silent Hill 2 was the best for me. Great atmosphere.

Dead Space is a great one.  Also, S.T.A.L.K.E.R is a creepy game, but I'm not sure if that's available on the Mac or not.  And yes, Silent Hill 2 was absolutely amazing and scary.  I also want to say there was another game that I dreaded playing by myself, but I can't remember which it was.

Condemned, Condemned 2, The Suffering, Manhunt, Dead Space, System Shock 2.

" It goes without saying. "

" @RecSpec said:

" It goes without saying. "

Godammit, I wanted to post that. "

• Dead Space
• Condemned
• Condemned 2
• Silent Hill

if you're gonna go current gen console game Dead Space is the way to go. It has a good narrative. The sound design will scare the shit out of you. I am a huge fan of the horror game genre but I wasn't able to play that game in the dark.

Also, Resident Evil 4 can be pretty scary and has a decent narrative.

My vote goes to Silent Hill 2. 

To this day, I've never had the constant sense of dread--and, concordantly, the exhausting jump scares--in a game like I had with Doom 3. People knock that game for it's design, but the first time through, I guarantee you'll always be hyper-tense. Especially if you don't fiddle with the genre too often. 

I wish you weren't limited to those platforms, because Eternal Darkness is pretty damn scary. But the other recommendations here are ok as well.