Game of Thrones

[Hindsight was 2020]

There are two big mistakes that seemed to of doomed the show once they ran out of source material: Removing FAegon and the changes to Sansa/Stannis storylines in S5. Book readers used to hate the FAegon plot because it felt like such a late addition but without him as we saw in the show Varys storyline and Danny’s downfall into madness both suffered greatly. An on the flip side Sansa/Stannis storylines completely did dirty one of the shows man characters and ruined their development for shock value (Sansa) along with butchering a plot live that was rich in the political drama that the show was known for (Stannis)

[Hindsight was 2020]

It's part of Martin's plan, apparently, for Danny to lose it, fwiw.

https://www.quora.com/Did-George-R-R-Martin-always-intend-for-Daenerys-to-go-mad-and-burn-Kings-Landing-to-ashes

Dany going mad isn’t the issue as much as how quick it does and the series of events leading to it. Case in point there is absolutely in-show logic why in the general public was so hostile to Dany, Cersei had used her status as queen mother just seized the thrown in a world where any distant male cousin of Robert would be viewed as more legitimate and had just nuked the equivalent of the Vatican in the process killing a popular religious figure (high sparrow) and “the people’s queen” (Margaery). By all accounts Dany should of had a sizable part of the general population welcoming her as a liberator but because George intents for the public to reject Dany to set her down a crazy path the show stuck to this idea even though there is a reason in-book for this to logically happen that the show got rid of (FAegon)

[Hindsight was 2020]

Just watch the first six seasons, and call it a night after watching Daenerys' fleet sail toward Westeros.  Let that be the last image you will have of the series, and pretend the last two seasons don't exist.

Season 6 also sucks

As does season 5.

Really, you're better off watching the first three seasons and leaving it there. They form a fairly complete narrative arc on their own.

First four.  Danaerys' arc in season 4 sucks, but season 4 completes the John/Ygritte arc with one of the most awesome episodes of the entire series, it completes the Arya/Hound arc in a very satisfying way, and of course the goings-on at King's Landing in season 4 are probably the best storyline in the entire run of the show.  It also has Pedro Pascal's best performance of his career.

Fair, I think season 4 isn't as good as the first three but it's still solid television. Everything after that... not so much.

The heart of the show is Tyrion's shenanigans in King's Landing.  Seasons 2/3 are the best because they have the most Tyrion in King's Landing content.  Those scenes have the best dialogue, the most intricate plots, the most humor and the best acting, they're some of the best TV ever produced.

Season 4 is the climax of that storyline.  After that the show completely falls apart.

Also with Tywin death in S4 the show had really began running out of really interesting villains besides Cersei especially after they completely butchered Euron