I think 1-6 are terrific overall. Season 5 gets a lot of flack, but I thought virtually every storyline outside of the Dorn stuff was awesome that year. Dany having to deal with SOH- great. Jonathan f'n Pryce and the Faith Militant vs. Cersei- even better. Snow aligning with Stannis and Davos- some of the best stuff of the season. Snow succeeding where Stannis' hardliner mentality failed and winning over the Wildlings to the bigger cause, terrific. That scene where he frees Tormund is probably among my top 10 favorite scenes of that season. Hardhome- one of the GOAT GOT episodes. My man Friendstone working his way back to Dany, very good, culminating with the Fighting Pits/Massacre at Mereen, another memorable, very effectively executed sequence.
Even the very offputting Ramsay/Sansa/Reek stuff was effective in the sense that Iwan, McElhatton, Sophie, and the always reliable Alife turned in compelling performances. I hated the direction they went with Stannis' character and his actions toward the end of that season was easily the most disturbing scene of the series for me. Poor Shireen.
I really enjoyed Arya's arc that season too because they did a good job, in the earlygoing, of presenting the House of Black and White as a weird, mystical place shrouded in mystery. Tom Wclaschla did a great job as Jaqen and Maise was consistently strong in the role. It was fresh in a way that it would not be in season 6 when the storyline began to drag and then go over-the-top with The TermiWaifer relentlessly pursuing Arya through the streets.
6 was an even better season. Battle of the Bastards and, even more so, the final episode of the season are high, high upper-tier episodes for the series. So when you are still pulling off that caliber at that point, it's impressive. Even a lot of the earlier episodes that season were good, particularly once Jon was back and when you started to get somewhere with Dany winning over the Dothraki. Everything in King's Landing was quality. Particularly enjoyed Jaime and Cersei conspiring with Kevan and Olenna to take out the High Sparrow before he made Margery do the walk of shame, only for that plan to be thwarted.
To me, it's really 7 and 8 where you start to see the dropoff in quality. I think people tend to point to a gradual decline after season 4. For me, I don't really feel it. I would wager to say that if you watched the show all through in binge-type fashion, the dropoff from 4 to 5/6 would seem negligible, while the drop from 6 to 7 and 8 would seem like a steep fall off a cliff.
And I'm saying that as someone who genuinely liked aspects of season 7 (particularly the phenomenally well-rendered squash match on episode 4) and who disliked season 8 to an extent that was less venomous than most people tuning in. It's just that season 7 really starts to meander before getting outright silly with Snow Patrol bro-ing out beyond the Wall going to get a zombie to bring to Cersei. Season 8 just messed up so many characters. Even if you like individual episodes to an extent or parts of individual episodes, it's just impossible to ignore the character assassinations:
If you look at Tyrion as a character, you can legitimately make the argument that once he kills Shae, he becomes a useless figure. The guy who was the smartest man in the room and one of the most effective at the game becomes not just less effective but outright actively shitty at his job. Season 5 he still has it- he might be a broken man because of how things went down in KL but he manages to negotiate well against the slavers, convinces Dany to spare Jorah, sells his adviser skills, etc. But from season 6 on it's bad, bungling decision after bad, bungling decision.
And here's the kicker. They set it up that every mistake he makes, Dany has to bail him out. He fucks up by cutting a deal with the Wise Masters and the SOH, despite Grey Worm's and Missandei's protestations. They just use that as a smokescreen, consolidate their resources and besiege Mereeen. Dany saves his ass with the dragons and the Dothraki. He sends the Unsullied to attack the Lannister forces at Casterly Rock, only to be outwitted by his brother of all people and get a major part of the army stranded so that Olenna and her crew are vulnerable to attack. Dany has to clean up the loss of her major allies in the Tyrells and the Dornish/Iron Born by cleaning house with Drogon and the Dothraki, dealing a major blow to the Lannister army and convincing both Jaime and Bronn (quite rightly) that the Lannisters will lose if a battle for King's Landing were to go down.
So Tyrion screws up, Dany has to fix it. And then the show has the gall to make it like Tyrion's missteps weren't that he was screwing up strategically and costing his Queen each time out, BUT instead that his major misstep was carting his wagon to that Dragon in the first place. Oh man she's an evil dictator- we saw it coming and we didn't stop her! Get out of here.
So that's bad. But he's not even given the worst of it. Jaime and Dany were completely ruined. It was not merely a case of fans being pissed because they got outcomes that defied what they had hoped for them. No, it was about a lack of adherence to longstanding character traits. Jaime was showing growth for years. He became an empathetic character and finally walked away from a destructive relationship in order to fight against the Army of the Dead. As soon as that shit is over, he is ready to go back to his sister cause...I don't know, toxic love I guess. Insanity. Here's a guy who fights to save humanity when his sister would not lift a finger to help. A guy who knows that she told him to screw off when he opted to leave her. A guy who knows she outright hired Bronn to kill him. And he's gotta go back there because he wants to die with her? What in the hell?
And Dany- just as bad, arguably worse. She commits the greatest-scale atrocity in the show. She commits genocide. She KILLS innocent civilians, including women and children which she was always very particular about protecting and helping and then she's leading fascist rallies and ready to torch anyone in the kingdoms who does not accept the New World Order. And why? Because Jon found their liaisons creepy once he learned of their kinship? Because she knew he was a Targ and felt threatened? Because she's batshit crazy like Targs sometimes go? A combination of all. It didn't add up. Look, there could have been a way that Dany's actions were devastatingly bad without making her fly up and down the streets and torch every poor fleeing soul that wasn't part of her army. You could have had her and Drogon accidentally set off the wildifire and it causes pockets of explosions that harm countless people, for instance. But to have her do what she did once the Lannister surrendered the city? Ludicrous.
Factor in other elements of the season like the way the Long Night battle went down, the fact that Bran ascended to the throne despite not doing anything to help anyone, the fact that Jon was a virtual nonentity for long swaths of the season despite the fact that he's the rightful king, and you have a lot of things that went wrong.