Shakespeare wasn’t even that good of a writer. There are better writers, more modern ones, like Stephen King and George RR Martin.
George “Let’s ignore half of history, take a superficial misrepresentation of the other half, sprinkle some sexual violence and betrayal over it all, then let everyone claim it’s historically accurate” R.R. “The Dothraki were actually fashioned as an amalgam of racist stereotypes I didn’t bother doing even the least bit of research on, but will pretend were an actual historical inspiration” Martin?
Not throwing shade on GoT as a work of fiction, mind, as long as people are aware that it’s solidly in the realm of fiction. Its popularity alone attests to its literary quality. A piece of fiction doesn’t need to be true to reality to be good (that’s the point of fiction, isn’t it?).
You do have to consider that the two unwritten books have the capability of affecting the previous books. Its hard to say that its a great series at this point in time, at least in my opinion. It definitely could be, I’m hoping someone with a better work ethic will take over when GRRM passes on.
They only have such a chance if they are every written, and I doubt they will be