Exactly As Advertised
The advertising for this film lays out exactly what you get from it, the documentation of a preachers final exorcism. If you watched the trailer, or read any print about it, you would have known that it was... ah, forget about it.
People are bashing this movie because they weren't scared, or because it was "documentary style", or because it was filmed from the first-person. Research your options before going to the theater if you don't want to be disappointed.
The only misleading thing I've seen is the image with Nell seemingly clinging to the walls. In the movie she is atop a bookcase or shelf of some type. The advertise presented the film as a bit of a mystery, and it is. The only thing is it gives you all the answers, but like the good Reverend the movie-goer will likely dismiss them as foolishness.
That's the good thing about this movie, it makes you think and examine your beliefs. The tag line about believing in God and the Devil works well for this film.