I loved it, really freaked out when I watched it at the cinema, perhaps on a small TV screen it doesn't have the same effect.
There was actual screaming when I went to see it from the majority of the crowd, never heard anything like it at a 15 before. Never really heard anything like it at an 18 certificate either.
I'd give it a healthy 3.5 out of 5. For Horror fans I'd definitely recommend it.