I enjoyed the movie having read the book, but I think it would be really difficult to enjoy otherwise. Movie moves way too fast. It includes all the most important "scenes" from the book, nothing is left out, the stuff that is in the movie is quite faithfully translated from the book.
Unfortunately it moves far too quickly. It could have stood to be another hour long, then it might have been a more moving story. Its not supposed to be about a kids triumphant ascent to military leader, its supposed to be about a kid's forced descent into depression and madness.
The movie needed more peter (he was literally on screen for about 60 seconds total).