>>212695001 (OP)I will give my absolute honest opinion.
I have this headcanon where it ends with Season 4, except that Tywin kills his traitorous dwarf son (or, depending on my mood, the two talk it out and go on to rule as father and son and eventually Tyrion ends up on the throne), kills the high sparrow as soon as he dares to make even the smallest move. I also imagine Cersei marrying Loras, which makes me laugh out loud imagining them trying to make a baby.
I could go on, but suffice to say, season 5 - 8 is in my experience poorly written fiction by D&D, with a few good parts sprinkled in there.
I can actually watch those last seasons and enjoy them for the low-quality they are. Interestingly, I cannot do that at all with the Disney Star Wars sequels, yet I can do with Rings of Power. Funny how that goes. Sometimes some slop can be retarded but it can still be fun to watch these trainwrecks unfold.
In the case of GoT S5-8 it's a mix of trainwreckery, absolute retardation, character butchery, with small whiffs of still genuinely decent scenes and good character moments (extremely rare, but there it is). For example: Brienne being knighted by Jaime and Brienne writing down Jaime's great deeds. In isolation, these are good moments. With season context, absolutely hilarious because of other moments, e.g. Jaime stating "To be honest I never much cared for the people, innocent or otherwise".
In a way those later seasons are fascinating. But they are absolutely not "canon".
ps in many ways I feel Season 1 is the only season that mostly adhered to the books. There are already some major problems occuring in Seasons 2 - 4 when taking into consideration the source material and even the trajectory of the show itself. But the quality of seasons 1 - 4 is, I believe rightly so, considered by many to be consistently very good.