I read the book after I'd seen the movie and was disappointed in the movie. It left a lot of things out, added some stuff and really obscured the timeline.
The book however was captivating, I really had a hard time putting it down, and it's a very easy read. I enjoyed delving more into Susannna's mind learing what she was thinking during certain events in her life. It also puts a light onto early psychological techniques, which thank God have improved. One of my favorite parts in the book is were she starts to see her hand withouth bones, something that was mentioned shortly in the movie. The characters are thoroughtly mentioned in the book and even some you didn't seen in the movie, the funny thing is that Lisa the Angelina Joeli character didn't seem to play as big of a role in Susanna's life there. The movie seemed to focus maybe too much on the character since she was the more practical Hollywood mold, while the book of course is focused on Susanna.
Anyway, it was a fun book to read and an easy one too, if you liked the movie you should read the book to learn more about what really happened to Susanna during her stay at the hospital.