Honestly, I find amnesia's atmosphere to be the most daunting thing about it. The ambient sounds keep you wondering. With dead space, its an action horror, so it's not going to be as scary as a survival horror. Never played outlast, so i'll take your word for that one.
Some horror games that i would highly recommend are:
Resident evil 1/2/3. Because you can never tell what's going to be in the next room, and its a survival horror, meaning fear comes mostly from the threat of running out of ammo or health. And you have to be careful saving, because you need ink ribbons to save at save stations.
imscared
http://gamejolt.com/games/other/imscared-a-pixelated-nightmare/10058/ is a free indie horror game that's pretty good. It might not be up to your level, but its worth a try if its free.
Silent hill series - just....no need to explain this one. These, next to resident evil, are the best survival horror games ever made. You can say horror games are never good if you haven't played these.
I see you: another free indie horror game
http://gamejolt.com/games/other/i-see-you/13843/among some others that i'm not gonna go hunt for links are
among the sleep: a horror game where you play as a baby. genius.
condemned: criminal origins.
and alan wake.