In most ways, “The Last Exorcism” is not a typical horror movie. Whether that’s a good thing will be up to you.

The first thirty minutes or so, in fact, are nothing like a horror movie. In documentary style, complete with several interviews, we meet Reverend Cotton Marcus (Patrick Fabian) and his family. Cotton’s father, an evangelical pastor, groomed him since he was a young boy to be a dynamic preacher and healer. Cotton can whip a congregation into a passion with the best of them.

Problem is, he no longer believes.

For years now, Cotton’s faith has been an act. That includes the many exorcisms he has performed. He goes through the motions and the “possessed” believe they’ve been healed. Faking an exorcism seems immoral, but Cotton provides a completely valid justification: he provides a service to people who believe they are possessed but whose ailments are actually psychological.

But now, Cotton wants to expose the truth about exorcism. Producer/sound technician Iris Reisen (Iris Bahr) and her cameraman, are going to document Cotton’s last exorcism. He shows us how he rigs up the bed to shake, hides speakers to play demonic sounds, and shocks the “possessed” with wires embedded in his rings.

This is all very interesting, but it doesn’t sound frightening, does it?

“The Last Exorcism” doesn’t even attempt to scare the audience until halfway through the film. Most horror fans won’t have the patience to wait so long for the goods.

I, however, found it to be a fascinating character study that sets up the second half perfectly. Because Cotton’s second problem in this movie is that he has run into what seems a genuine possession. (We wouldn’t have much of a movie if he didn’t, would we?)

The possessed is a 16-year old girl named Nell Sweetzer (Ashley Bell), whose father, Louis (Louis Herthum), has sheltered her in every possible way since Nell’s mother died a few years earlier. Nell appears to be innocent bordering on angelic. Nell’s brother Caleb (Caleb Landry Jones), however, seems like the hellion. He practically attacks Cotton when he first arrives and threatens the preacher’s life should Nell get hurt.

For most of the movie, we aren’t sure whether Nell is really possessed or not. She could very well be acting on the trauma of losing her mother and living under the thumb of an oppressive father. It’s also possible that Caleb or Louis is committing the horrible acts that originally brought Cotton to the Sweetzer residence in the first place. The nightmare Cotton has stumbled upon could be of the dysfunctional family rather than the Satanic variety.

The faux documentary style helps to keep us guessing, but the superb acting is what sells the movie most effectively.

Fabian is perfectly cast. He is smarmy and hateful at times, yet we soon realize he is just a good man who lost his faith.

Bell completely steals the show, though. She shifts from frail, pitiable victim to menacing beast with stunning ease, and she is as convincing playing a child as she is playing a demon. Horror movie roles rarely offer an actor the chance to show that kind of range, and Bell makes the most of the opportunity. Expect more from her.

The strongest quality of “The Last Exorcism” is that it keeps us guessing. Nell’s condition and the dynamic of the Sweetzer household seem clear enough early on. Until we discover things aren’t what they seem. And later we’ll learn it’s even more complicated than we thought.

The biggest weakness is that there just aren’t many scares. And when it finally develops into a full-fledged horror movie, the shift from understated fake documentary to full on horror is a bizarre leap that might seem like we’ve jumped into a completely different film.

Ironically, those who don’t usually like horror movies may like this one better than the true horror fans.

Jeff Marker is a media studies professor at Gainesville State College.