If I didn't read the book, my rating might have been higher, but there were lots of scenes from the book that I would have enjoyed in the movie. For instance, most of the book is about Nathan trying to find out who A is. I would have loved to see that, but unfortunately they cut it down to just a few scenes with Nathan. The acting was great and what was presented was good, but if I had to choose between the movie and the book, I'd pick the book. So if you get the chance, read the book. You'll really enjoy it, especially if you enjoyed this movie.
