This movie just seemed to lack direction. The plot developed so many twists in such a short amount of time that it seemed to lose any semblance of what the true storyline was. There was a lot of wasted dialogue and just seemed like the writing was rushed and a little too wandering. The exorcism scenes and possession story began to take a back seat to the character's back stories (which were a little weak to begin with).
All in all, I would say skip it unless you have rented out the rest of the horror section at your local video store and you have a jones for a movie you haven't seen before. You're much better off just watching The Exorcist or The Exorcism of Emily Rose.