The movie differed from the book in quite a few ways and lost some of the important underlying themes. That's not to say it wasn't good in it's own right, just different.
It was funny and kept me entertained the whole time. Unlike many people, I didn't find the violence that over the top. There have been plenty of movies just as violent if not more.
Overall, it was a movie that I don't regret seeing in theaters since I like supporting these kinds of offbeat movies.
My one gripe is that the music is extremely heavy handed. Much like visual effects, if you notice the music, someone isn't doing their job.