One of my main gripes with st and how the duffers worked the supernatural is what they did with the mindflayer.
Imo, the mindflayer should've been something that was at best theorised post s2, hell thats all they did in s2 and it was perfect, it being something the party can only guess at was amazing, interesting in a way that they didnt manage to replicate at any other point, and they killed all its mystery in s3. Also, it only being properly known by Will had so much potential.
To add to that, I think the supernatural plot of s3 and s4 should've been switched (and s3s supernatural plot redone a little).
To go from the plot of s2 with "holy shit this is all a hivemind and the flayer plays some kind of role in it", to the plot of s4 where now the cast thinks they've got all the answers, "vecna possessed will, vecna controls the hivemind, it was all him, 001, Henry, Vecna, he's the ultimate monster, the one we couldn't kill" and THEN to the supernatural plot of s3, where now after failing to kill vecna, people are being flayed, possessed like will was in s2, and this time they rationalise it to "we didnt kill him, all this is him".
And the best part of it is that when theyre finally facing off against the s3 body of the flayer, they would be confused. I mean, what sense does that make? to them, facing off against Henry would've been the expectation, not this giant meaty thing that only seems to spark recognition in Will.
And I think that with its "defeat", that would've led into a completely redone and rewritten s5 perfectly.
To end s4 (with s3s plot) with all these hanging threads, that in this case would've been perfectly plotted, would've been so much better because this time the writers wouldn't be that backed into a corner, vecna can stay impossibly strong after being given a whole season to rethink and plot, meanwhile, the mindflayer ends up the big bad they NEEDED it to be.
With THIS set up, the characters finding out they were wrong about EVERYTHING brings the intended doom and dread i think the suffer brothers thought they achieved.
And it'd make more sense too because this time they truly would have all shown assumptions dead wrong.
