Yes, I had read the series before the show started and was so excited when I heard they were making a TV show based on them. I had loved the books, but this is weird: in almost every other instance I can think of, I think books are far superior to the shows or movies based on them; with GOT, I actually think that the TV series is more satisfying.
The main reason is that Martin gets lost in too many side characters, creating some “voice characters” who are very minor and sometimes short-lived characters who are not even featured in the show or are relatively minor (like Davos). When I say voice character, I mean that Martin organizes his book with a chapter from one character’s perspective, then the next chapter from another character’s perspective, etc. Two of the books do not even feature some of the major characters. And he could use an editor to chop out extraneous scenes. The show makers agreed with me on which scenes to keep and cut. And the way that scenes cut into other scenes featuring different characters on the TV show is a really natural fit for the way he wrote his voice characters, and we did not have to go a season without learning what was happened with, say, Daenerys, unlike how I had to read a super long book that did not mention some characters I cared about!
Also, he seems to have become terrified with writer’s block since the show became a hit. He still has two books to write and there has been no publication in all these years! (He did publish a separate “history” of his world— kind of getting side-tracked). I can’t imagine being an author and letting the show makers be the first to reveal the end of my story, losing control of my narrative.
But I also think that the dialogue and overall show have weakened in the last couple of seasons since they left the books. The show writers are a bit more into spectacle and are not quite the masters of character and dialogue that Martin is, although I still am loving the show and look forward greatly to seeing what happens. And some of the parts that were new to the show, like Cersei’s revenge on the High Sparrow and company (she had just finished her walk of shame in the books) were pretty well done, so credit goes to the show makers!
It was gratifying to see that some of my hopes and predictions from the book were realized by the show; in the books, Jon Snow appeared to be dead, and I was hoping he would turn out to be alive and would be the son of Lyanna and Rhaegar… so that was fun when those things actually happened.
Oh- there is no Night King (yet?) in the books. The White Walkers do not seem to be as “coordinated” in their actions in the books- at least not yet.
And Sansa has never had a heroic moment in the books, and it was Jeyne Poole (a childhood friend of Sansa’s), not Sansa, who was married to Ramsey Bolton and whom Theon helped to escape.
One thing from the books that did not make it into the show that I think should have: Tywin and Jaime had lied to Tyrion about his wife, who really had been an innocent farm girl who loved Tyrion, not the gold-hungry prostitute they told Tyrion she was. When Jaime frees Tyrion, he admits this in a fit of guilt, and Tyrion is angry at Jaime and then this is the main reason he murders his father.
I would recommend at least the first book to anyone. It is very well-written and the show was pretty true to it. But I think many readers plowing through all five books (so far) may become frustrated in some parts. On my rereads, I skipped some voice characters’ parts altogether and just reread those of the characters I find most compelling.