The Last Exorcism

Okay folks, since this one is still in the theaters, I need to be careful about what I post. But judging that my previous post has not been read by one single person, I can probably post whatever I want, and you'll never know.
So the wife and I went to see "The Last Exorcism" this afternoon. I'm picky about the horror films that I want to see, and this one didn't qualify, but the wife wanted to go, so off we went to the 4:45 matinee.
The movie starts out well enough, being filmed as though it's a documentary. The movie actually kept my attention the entire time, and I was never bored or disinterested. The suspense was good, and I was always curious about what was going to happen next. The creepy parts seemed to have just the right amount of creepy. I'm not certain how long the movie was, but I was thoroughly entertained until the last 5 minutes.
The last 5 minutes got really weird, really quick. Neither my wife nor I fully understood what was happening, or why. Then the movie just ended. Abruptly. All in all, I was going to give the movie a B+, but because of the last 5 minutes and the ending, I give it a C-. We think we figured out what was going on during the last few minutes during our drive home, but we're not sure, and the movie certainly didn't make it clear.
Ultimately, my opinion is that this movie would be okay to rent, but not under the "New Release" price, and it might even be better after the consumption of alcohol. So, in a word, I would describe this movie as "ehhh."