The first say twenty minutes weren't that bad at all. Somehow the director succeeded in picturing the boredom of blasé teens very well, like "chilling" together without a clue how to fill the time or what to talk about. See for instance how they morosely hung in their seats in the haunted house, before the things got rough. There's also a short but brilliant scene when they stop at a gas-station to buy condoms, and the guy at the counter insists on giving an educational demonstration, really hilarious.
But this movie set out to be a horror flick, and here it failed completely. The premise was far fetched to begin with (but hey, what horror-premise isn't?!), and the subsequent goings-on were ludicrous and totally unscary, not even amusing in a campy sort of way.
In short, a superfluous wannabe horrorflick, with in a few scenes the shimmering of real cinematographic potential.