Seeing and hearing something dangerous but having no idea what it is, or not having a way of fighting it.
This. Fear of the unknown is one of the biggest and most misused aspect of horror, I believe.
The best horror is very psychological, it shouldn't rely on gore and shock scares. It should mess with your head, make you feel like you're in a situation completely out of your control, and make you deal with something completely alien to you (zombies aren't alien to us anymore, they're a tired cliche). It's just very, very hard to pull this off.
That's 1 and 2 covered.
3) It's entire routine is old and stale already, and it's been ruined by dorky design.
4) Only played it briefly, but it's rough quality really made it hard to get involved in.
5) Obviously no, but it all depends on how great the actions you repeat are, I suppose.
EDIT:
1) Nothing. Movies and games aren't scary.
Ooh, big man Urby.
There's still some classics out there, probably better known for being more unsettling and a class above slasher/zombie/splatter shite. I'm thinking The Thing, Jacob's Ladder, An American Werewolf In London, films like that, and games like Eternal Darkness.