I think there's a ceiling on how scary a game can get by the traditional rules. You can only have a revolting monster jump out with scary noises and try to chomp your head off so many times before it gets old. Once it's too scary it just can't get any scarier with that medium. Although I'm not a big fan of "pop-out-and-scare-you" games like the ones you mentioned. I'm more into fighting normal regular human people that I can imagine shooting in real life. I can't imagine shooting a half eaten corpse with tentacles writhing from it's body in a dark, wet, smelly corridor.