I was still on board till toward the end of season 8 but season 7 was obviously a significant dropoff in quality from the very solid season 6. It's just many of us excused it because we knew there was still one more season to work with and potentially improve things (they're going to take two years to make it, it's GOT TO BE GOOD...).
Season 7 still had its good episodes and moments. That episode 4 battle, like you said, was really well executed. Season 8 even had a couple of good episodes and moments. But when you have a great series, you really should be sticking the landing and season 8 certainly did not do that. It crumbled in the big moments. Long Night battle- a jumbled mess that even the GOAT GOT director could not salvage.
Not only that but all that build up for Frost Maul and co. and they were treated like a co-main event on a Conor McGregor card. Hell, like a co-co- main event since Weiss and Benioff rapid-fire played it like Frost Maul is the big bad, no Cersei is the big bad, NOO Dany is the big bad. All within three episodes. Rushed, ridiculous stuff.
Dany's heel turn was handled in a terrible manner. No nuance at all. And executed in the most ludicrous way possible. She goes from someone who protects civilians, particularly women and children to someone who goes scorched earth deliberately on citizens. Not only does she not have qualms about killing them but she actively goes out of her way to kill them, prolonging the siege when the Lannisters already surrendered so she can do grid lines across the city nuking everything in her path rather than, you know, flying straight to the Red Keep and killing the person she actually has beef with.
But y'know Targaryen, something something, flip a coin, something something, burn them all, something something.
It was just bad. The failure of episodes 3 and 5 on that season were so significant that the entire season was a wash. And the final season should have been, at the very least, satisfying.