Decent watch at best, won't watch again, and can't honestly recommend.
I was excited to randomly find Janel Parrish (Mona, "Pretty Little Liars"), and she's clearly a higher caliber actress than this movie, she sort makes the actors that are doing good look a bit off.
Jennifer Stone does crazy in a wonderful way, but she's so crazy for so long, there isn't much in the way of character work that isn't directly distracting, as they are mostly attention seeking self destructive teen actions.
The movie is also a bit scattered in the plot direction. The title would suggest it's about a possession, but it turns more into a psychological analysis of teenage girls exposed to morals in and out of religion.
It gets preachy, but not in any of the fun ways, well, maybe one of the fun ways.
It's not that is doesn't have some good things about it, but just not enough that I think you shouldn't be watching something else.