I just finished "Angels and Demons" this past weekend and I agree with Mary's analysis. It was captivating in parts, but often I felt like I was on a merry-go-round, reliving the same scene/plot over and over. Brown's ideas were interesting, but I felt a bit too fantastic in parts (Langdon jumping out of a helicopter without a parachute and actually surviving? Not to mention being able to get right back up and run back to the Vatican...). And certain aspects were just overwhelmingly gruesome or sexual.
An interesting read, but definitely not stellar literature.
P.S. My husband and I just watched the movie. This was one of the rare times that I felt the movie was actually better than the book. They deleted ALL the sex (thank heavens!) and it was actually very entertaining. I might even go see it again. :)