Overall, if you walk in understanding it's not going to be incredible, then you are fine. It's actually decent. However, most people walked in thinking it would be great...big mistake!
Great approach. I really liked the back-story of Cotton Marcus. Having a preacher that doesn't believe was a great concept. The acting was incredible from the young girl (who I swear must be Michael Cera's sister). But the inability of the writer to maintain intensity during the "possession" scenes was a disappointment.
Plus, the ending was abrupt and sort of from left field. It was VERY unexplained and left the movie on a bad note. After all, the endings are the most important.
The biggest thing for me was that they stayed at least FAIRLY close to the book. My requirement was met. When I read New Moon last summer, I was going through my own "Edward leaving" problem. I connected to this book most of all. I even had a Jacob in the picture. For them to successfully pull this book off meant the world. It was great...now I just have to figure out what to do now that my Edward walked back into the picture...