Speaking just for myself here, but my major beef with the writing is not the direction of the plot. It's the dialogue. This series went from Academy Award-level writing the first two seasons all the way down to Asylum-mockbuster level writing this year.
Well, that, and the casting of Euron. For the most part, the kingsmoot was well written and well acted. But when Euron stepped up, it was a train-wreck. It was almost like they prioritized getting an actor who looked like Theon over getting someone with actual acting ability. When he jumped up and said, "Where are my nephew and niece? Let's go murder them!" it was the most cringeworthy moment of the entire series. Bad acting combined with bad dialogue! Ugh!