Seasons 5 and 6 were noticeably worse than the first four, but I still enjoyed them. Season 7 was bad, but not show ruining bad. Had it gotten even a decent season 8, I think it would have been an amazing show all around. Not flawless 10/10 material, no, but still a great show.
Season 8 was honestly impressive in just how many plot points it threw down a well. Jamie's redemption? Nah, screw that noise, he changed his mind. And I don't think I've ever felt so deflated after S8E3. 8 years of buildup and that's how they end it? What a monumental waste of time it turned out to be.