I first saw the TV show earlier this year, started the books after watching the show and finished the 5th one a little while ago, and I have to say that while there are obviously some advantages for the book (the depth of world and history that the show can't realistically provide), I think the show does many things better, including (and in fact especially) when it makes changes / additions. One of the main things I'm looking forward to is seeing the TV show do the storyline for books 4 and 5 as I expect there will be quite a lot of changes and storylines condensed, and I think the story will be better for it.