Watched it last night having just read the book. I found it followed the book very well, but I failed to see why Sean Penn earned an Oscar for his performance. All the acting was good, but I found Sean Penn a little cheesy at points and unable to correctly convey the persona of Jimmy in others. I felt like Penn portrayed Jimmy as more of a villain, where as in the book, his actions are explained and somewhat justified. Also, they don't delve much into Jimmy's past, where a lot of his character development comes from. Overall it was a good film, I would recommend reading the book to compare.