It's one of the best. Don't listen to the haters.

Rating: 9/10 (16 January 2013)

I don't know what people are so peeved about that they even create accounts just to down vote this. If this doesn't scare you, I think you should stop bothering. I'm not saying everybody will get as affected as I did but if this movie really does not scare you at all, which one does? Seriously, message me and tell me.
I'm not a huge fan of horror movies because there usually is a killer, zombie or some lunatics involved and that does not touch me at all. Like some said before: It's so scary because you cannot see it.
You need the right mindset for this. First of all (as you should always do) keep your expectations low. Don't expect to get shocked every time it seems to happen. I think a lot of people couldn't handle the very slow increase in suspense (and some are probably just those guys, who start making fun about everything that's happening on the screen because they don't want to get scared but look like the tough guy instead).
P.S. The 2nd one is really good as well, 3 & 4 kinda do the same thing but with dull endings.