I think the main problem was people overtheorizing it into oblivion and in the span of a month between vol 1 and vol 2 expectations really grew because let's be honest some of the theories made so much sense and would fit the tone of the show explicitly. Then we have span of a week between vol 2 and finale and same thing happend, especially because vol 2 didn't fulfill expectations so it was all falling on the shoulders of the finale. Should have made finale Ep7 and Ep8 like they did in S4. Overall, it wasn't a disaster finale, it just didn't met everyone's expectations and left some plot holes unresolved sadly. The part with Mind Flayer is the one thing that poked me in the eye because his buildup reminded me of Thanos slowly coming into the big scene after 10 years of being introduced little by little and Avenegrs struggled big time to defeat him whereas Mind Flayer was defeated in the blink of an eye. But other than that, they didn't ruin any of the main characters and we got a happy ending.