The Last Exorcism is a fake documentary, in the style of REC, The Blair Witch Proyect and others.
It's about a very friendly, simpathetic and funny priest who has lost his faith and now performs fake exorcisms to show the world how false are this practices, in a documentary he's making. Previsibly, he eventually comes across an actual possesed person, and he and his crew (a cameraman and a sonidist) have to face this dangerous teenager.
This film pretends to be a scary movie, but I'd like to see it more as a comedy. The first thirty minutes actually try to be funny on purpose: We see the exorcist and his crew not taking their "job" seriously, and there are various genuiely funny situations. There is a moment where the movie starts to try to scare us progressively, but it never really succeds. Well, I have to admit that's a matter of opinions, because there was a group of girls in the cinema who sreamed a lot, and were visibly scared. But most of the people in the group I was in were laughing their us off. Just like me.
The movie doesn't manage to get credibility and, among other reasons, this is because it starts off in a very campy way. Also, the director decided to have a lot of image and sound editing, wich doesn't make any sense at all if we are supposed to believe that this is a false documentary. If it was supposedly shot with only one camera and no planning, how the heck could there be any editing of any kind?
Anyway, this movie actually works if you don't take it seriously, for it can provide a really funny experience, so I will award it 4 out of 10. But we shall ignore the ending, wich is one of the most insatisfactory endings I have seen in a long time.