Some movies based on books just jump right out at you from the silver screen, some books just don't make good movies, and some are only good if you read the book first. Unfortunately, Babylon A.D. fits squarely in the last category. The movie is visually appealing, and the acting is credible, but nevertheless, only those who have already read the story are going to see any depth to this movie. This is the same phenomenon that happened with the Hitchhiker's Guide to the Galaxy. As it stands, it is only just OK because there is a lot of action throughout the movie, and the good vs evil theme is plain enough, but as it stands, it is still only two dimensional. Personally, it is a good candidate for a DVD rental.
This movie is never going to win an Oscar, nor is it an in depth look at psychological trauma. That being said, it was a very fun movie. The plot was reminiscent of the remake of "The Longest Yard" with Adam Sandler, "The Fugitive", Battle Bots, and maybe some Mad Max thrown in there. If that doesn't sound like fun, this might not be the best movie for you. I thoroughly enjoyed it myself.