Warning: this post may contain spoilers
So, in a nutshell, the writing quality and character development declined a lot in the last season ... except I mostly didn't notice (or mind), until I started reading online about how much - and why - everyone else hated the last season.
I got as far as S08 Ep03 (the White Walker battle) without reading any online commentary, critiques, etc. On my own, I did feel some characters' activities/behaviors were a bit 'off', but I still loved the episode overall (except literally too dark, hard to see some scenes).
Then a friend commented on some disappointing thing in the episode, and how 'everyone' was bitching about it. I started reading online ... and that's when I started seeing the flaws in the last season.
Granted, even if I had stayed offline, just watched it myself, there probably still would have been things that pissed me off ... Euron's magical dragon ambush, the whole Missandei capture/murder thing, and Dany embracing the Dark Side. I can't imagine I would have overlooked those.
But, by reading everyone else's gripes online, watching bitter youtube reviews, etc., the last 3 episodes sucked a lot more for me, because I saw all the flaws, many of which I would have missed.
So, to sum up, I blame all y'all for ruining GoT for me.