This would have been a lot better if it hadn't been presented as a "true story" based on "actual events." As a Catholic, I have no doubt the existence of demons and evil spirits. This guy makes exorcists look like circus sideshow freaks. For those of you who already hold that belief, go ahead and feel free to skip this movie altogether. It's not for you.
Having said that, it's an interesting work of FICTION as is perfectly entertaining as far as that goes. The problem comes when you try to associate this with reality. When they show the guy on whom this was based at the end, you lose all interest in everything you just watched. You're better off watching this as entertainment and stopping the movie as soon as the credits begin to roll. You'll feel much better about having spent an hour and a half watching this.