Not a bad movie... but certainly not the most captivating either. An interesting adventure of a crusader with a sense of repulsion, ethics and morals beyond blindly following the commands of the church. Some of the effects were good. I agree with one of the other reviewers that at some point, the movie becomes confused, and thinks it should be a horror.
I have to admit to being confused about the demon. He suggests that he had been been pursuing the exorcism bible throughout the ages, and that it had cost him heavily. Were that the case, it is confusing as to why he would not have just taken "THE" exorcism bible in the opening scene (he/she had the chance). Also, why travel to a monastery by road, when you could fly - and just find it yourself?
Besides a few logic errors in the script - it was a light and enjoyable movie. Do not watch with high expectations. It is more like a Wednesday night movie.