Game of Thrones is the sequel to the type of book that ends "And they all lived happily ever after"
This isn't a story that ends with "happily ever after". That's where we started. This whole series is the sequel to a book never written. A classic fantasy, about heroes who fought against an unambiguous evil, about people who took their lives and their honor into their own hands and stormed the gates of the mad king. The brave hero became king and married a beautiful woman, his friend and comrade returned home to raise his family in happiness in the keep of his forefathers, and they all lived happily ever after.
But the brave hero doesn't know how to rule, and the beautiful woman he married isn't just a trophy for being a legendary hero, but a real person with her own flaws and needs that he doesn't know how to handle.