Amazing. Captivating. So well-written. 
 I watched the first six seasons of the HBO show before I picked up the books, and while I knew everything that was going to happen in the first book beforehand, it allowed me to keep up with the characters much more easily (I've heard from several people that this is a big struggle for people who try to read the book first, understandably) and get a deeper understanding of their actions and motivations. 
 Like Harry Potter, this is a series you really have to commit to, but it's well worth the time.