I think the issue was mostly how lazy and simplistic everything was. Sure, it was unpredictable, but just doing unpredictable things without any buildup is not a good way to tell a story. Bran becoming King for example is an unexpected twist, but the setup is nonexistent and the reasoning is dumb. The Long Night only lasting about an hour was a massive anticlimax for one of the main conflicts (it’s almost certainly not going to be that short in the books). Most of the characters’ endings were predictable, but some were way too sudden to be believable; Dany’s random fall to madness is particularly bad. They also failed to use interesting plotlines in a meaningful way; Jon being the true heir to the throne is so utterly pointless that it literally could be cut from the show and nothing would change, for example. It doesn’t cause conflict at all beyond an incredibly poorly executed plotline with Varys that goes nowhere. Characters also became incredibly stupid and some lost any traits that made them interesting (Jon in particular is painfully generic by the end). It essentially went from a brilliant, complex show to trite people only watched for the action and/or to see what happened to the characters. The worst part to me is that people endlessly went on about it “not having a happy ending”, but everyone other than Dany, Jon and Grey Worm got a happy ending. The final few seasons also have utterly awful writing, especially dialogue. There’s a video on YouTube where someone edited the final episode to have no dialogue at all, and it’s about 20-40 minutes of footage with nothing happening.
Daenerys had to always be talked out of solving problems with Dragonfire. If she didn’t die, it wouldn’t be an ending because we’d be left with a question about whether or not she might someday go Mad Queen.
The point of the show is that it’s fairly arbitrary who sits on the throne. Robert Baratheon because he won a rebellion, Joffrey because he was supposedly the son of the King (but really wasn’t) his brother because Joffrey was poisoned, then their mother because… well she was an important person that was in the capital. Big army diplomacy, claims based on blood relations to dead people who were previously the monarch, fast army diplomacy… that’s basically a monarchy in a nutshell. It’s really the advisors that run everything so why does it matter who sits on a fancy throne?
So it’s fitting that it ends with someone on the throne being arbitrary, it’s ultimately what a monarchy is, just some arbitrary person that people agree is the person that site on the throne. And it was the point of the story. It’s all just a silly game the powerful play while the peasants die for because of it.
None of the decisions were bad, it was just rushed and clumsy. Just people didn’t pay a lot of attention to the fact that Daenerys was using dragonfire to solve her problems more and more. Didn’t pay attention to the fact that who’s on the throne doesn’t much matter, the most important thing is that people agree on whoever it is. Didn’t pay attention to the fact that the prophecy was just some bullshit that made Stanis do horrible things (like burning people alive) and didn’t notice Daenerys was going down the same path I guess they thought she was the real chosen one. People just didn’t pay attention to what the point of the story was, and were disappointed that there was never a real Prince of Light, just a bunch of assholes getting a lot of people killed for their petty game of thrones.
