I find that this book, despite the colorful use of vocabulary, to be a good book.
While this book deals with matters that most people would actually leave behind closed doors such as Karl's parents relationship, how loose his mother is, and the not-so-glamorous issues that some writes avoid. While there is humor in order to lighten the load, you can still fill the frustration that Karl feels as his mother's destructive behavior and his need to try and fit in.
But in the end, there is a light in the tunnel, and a small metamorphosis happens for the good.
John Barne's style is very fluid and rather believable as well as how in depth his characters are.
Though I wouldn't suggest 11 yr olds reading this, this book has a good discussion points a diamond in the rough.