I thought the movie was absolutely amazing! There are a few differences from the book, primarily in the beginning and also the end, but otherwise follows it very closely. The only part of the movie that was a little disappointing is that most of the main scenes supposed to be in St. Peters, St. Peters Square, Pantheon, etc... all are computer generated. Overall the movie was great and I would recommend it!
NOTE: I think the movie is a bit graphic, especially the killings. I was quite surprised to find out it was only PG13 and not R.