GRRM is a very good writer. I have read all the novels , books 1-3 are dynamite, 4 and 5 are very good but do contains some chapters that are tap dancing. Funny thing about George , even the tap dancing reads well, he is a natural born story teller and can engage you with a yarn.
Agree with you more or less completely (I thought 2 was a tad strung out, but I was amply rewarded by book 3, it was a fantastic ending. I was breathless! ) Yes his writing is excellent and is a huge motivator to read, even in following his more meandering parts.
I have seen fan criticism that the TV series started to go down in season 5 when they ran out of material, I did not find that true at all , season 5 had Hardhome and season 6 had Battle of the Bastards.
Only miscue I felt was the shows story of Arya in Braavos which was much richer in book 5 and even the excerpt we got from GRRM is better than it's treatment on the show.
Seasons 7 and now 8 have an air of expediency about them that was not the fare in season 5 and 6.
As I have said before 8 is showing seams that didn't used to happen.
I think the issue, or at least the way I have seen it described, is that the TV show has to force arcs to complete for the series to have a conclusion - and they have limited time to do it, while GRRM will have as much 'time and space' to complete the story arcs 'naturally' in the books.