You are entitled to your opinion.
From what I know of you, you seem to be an intelligent individual. I suspect that if you were to sit down and binge watch the series, you would find yourself noticing a significant quality difference in Season 1-4 v. the rest of the series. It is possible that you are not appreciating just how good the initial 4 seasons were. HBO did a fantastic job of bringing the books to the screen. They used some of GRRM's best dialogue, and made some changes (for the better) to some of his scenes/narrative.
Since running out of book material to lean on, the show has been poorly handled, IMO. Granted, they didn't have an easy task, and they are clearly doing something right based on the ratings. It could have been so much more, though.
As an aside to this post...
One of my favorite changes, that HBO made, was putting the Moon Door, in the floor of the Eyrie. In the books, the door was in a wall and Lysa was trying to push Sansa out of the door when Littlefinger stopped Lysa and pushed her out the door. In HBO's version, having a big hole in the floor made for a much more suspenseful scene. They also incorporated it into the scene with Bronn fighting Lysa's champion (Sir Vardis Egen). In the books, there was no hole in the floor during the fight. Having it there really added a lot and made for a great conclusion when Lsya says, "You don't fight with honor, sir" and Bronn responds, "He did" and kicks Sir Vardis' body out of the hole. One of my favorite scenes from the entire series, with fantastic dialogue. Proof that HBO is capable of doing great things without leaning on GRRM.
Maybe that bodes well for the spin off, since they will mostly be starting from scratch.