I watched the series first, then i got curious about the book. I was reading the 3rd vol, but I dropped. Its like Issybird said, he goes on and on untill the end of the book... on the last 100 pages everything that should have happened happens and the book ends.
About the tv show and the book: there is no significant differences between then. Some occasional changes just to make the series more fluide on tv, but no loss of sense. You won't get much more from the book. So if you want to know only the plot you can definitly watch the series only.