I really did think it was excellent right up to the end. I loved the premise that the guy was making a documentary to expose charlatans--didn't see that coming from the previews at all.
I would've gone more with 'deleted scenes from Rosemary's Baby' rather than Lovecraft, and "aww, c'mon, you were doing so well" rather than WTF, but yeah. Ditto, basically.
I hated it that the most striking visuals were spoilered by the previews, but I guess they had to do that to sell tickets. Last year I made a point of not watching any of the trailers for Inception. Going forward I'm going to try to do that more often.