Big thumbs up here. I saw this yesterday afternoon. I’ll post my own thoughts about the movie at some point. However, John Zmirak over at Godspy has written a review that says most of what I wanted to say already. (Note: his review does contain spoilers, but nothing that will take away from the impact of the movie).
One recommendation: unless you have committed yourself to a point-of-view that regards spiritual warfare as patently silly and medieval, go see this film as a matinee rather than late in the evening.
For more information about exorcisms, check out this website created by an exorcist.