it's not dumbed down too much
you will need to suspend disbelief for a few instances, but the camera work and the pacing is pretty great
it has a horrible coda (like the last five seconds of film) and it has at times a horrible screeching soundtrack, but it's rare, and there are other elements of the soundtrack which are really good.
i largely agree with the av club's assessment and i'm glad to see a horror film which could have been generic torture porn go a different route