If you look at the plot in its entirety, it's not an unreasonable scary movie, but the acting was very poor, and the sexual undertones (if you can even call them that, for as subtle as they weren't) were pretty cheap and exploitative. Not really worth watching, because it's not even bad enough to be funny either.
Interesting story, certainly, but it kind of portrays him in an unnecessarily heroic light, like oh yeah, your parents were screwed up, so you really taught them a lesson by doing something stupid (the ending tries to reconcile this, but it doesn't really make sense). This movie had a brush with true awfulness when Kristen Stewart showed up; I really thought he was going to sleep with her, just to piss me off and add nothing to the plot, but at least the movie dodged that bullet. Still, I've got my qualms with it.