Haha! rabboi, im not a forum moderator, you dont HAVE to do anything i say, but its good you moved it.
Personally I like the idea of one main monster that kills lots of people but you never really SEE it. As in, you see grunts fly past you etc as if the monster did it, but you dont see the monster itself untill the end. (think of the first Alien movie. How many times did you actually SEE the alien in full view? and THAT was the scariest one!)
Not having a lot of ammo also adds to horror (a trick brilliantly used in the resi evil games).
Darkness is used an awful lot in horror, but you can make things just as (if not MORE) terrifying in good lighting, because you dont expect them! Good sound effects in the background and constantly keeping thev player thinking that there is something around the next corner (with trails of blood, scratches etc) are other brilliant ways.
Its probably MORE difficult to make a 3d game scary, since you cant push the plot along in the same way a film does, but horror in games is FAR worse!