OK...my thoughts in no particular order:
1) I am so sick of movies/tv pretending blunt-force-trauma is not a thing. I'm a 6'2", 220lb grown ass man who can't slip on some wet wood on the back deck, fall the 3' to the ground and not break 4 ribs and knock the wind out of myself, but I'm supposed to believe that a 10 year old, 75lb little girl can get thrown across a room with enough force to shatter a full wooden bookcase and then get back up??? GTFOOH.
2) So, if the initial rumors were true, and there was a 2-3 year "time-jump" between S4 and S5, this wouldn't be on the list....but there wasn't. S5 literally takes place the very next year. So, someone explain to me how a miles-long inter-dimensional rift can rip a town in multiple directions down the middle, but in less than a year, the rifts are somehow magically "sealed" and the whole town goes back to normal?? GTFOOH.
3) I understand the need to keep 11 hidden, but what was the whole purpose of "The Crawl"? Did I miss a prequel?
4) On that note, it feels like there is a missing half-season that needs to explain how the fuck we got from the end of S4 to the beginning of S5. We are just supposed to accept all the shit that has changed with no explaination??
5) Watching scenes with Dustin, Jonathan, and Steve was like watching gender-swapped mean girls. JFC, when did they become such irritating little bickering bitches???
6) You can definitely see the off-screen animosity between Harbour and MBB leak onscreen.
7) Turning Nancy into an insufferable bad-boss-bitch fell flat. Her lines and attitude were textbook Mary-Sue.
8 ) Don't get me started on the firing a delicate glass tube filled with intricate electronics out of a fucking shotgun, not once, but TWICE, with no ill effects whatsoever. GTFOOH!
9) Let's talk about the sheer amount of Deus Ex Machina they shoved into this: In the entire upside-down, 11 just happens to stumble upon the exact spot where Hopper is. Dustin just happens to wander down the right road at the right time where Jon and Steve are. Joyce just happens to drive down the right road where Robin and Will are riding. And I don't want to talk about Murray just showing up like a fucking Amazon delivery-man with just the right collection of random, weird-ass shit that they all need for the gang's wacky plan to succeed. GTFOOH!
10) Both MBB and Sadie (Max) got thicc in the off-season. But they tried to hide it on 11 by sticking her in sweatpants and track shorts (LOL...fail) but leaned into it with Max by dressing her as a rugged outdoors-woman, which worked perfectly.
11) Whoever wrote Robin's (Maya Hawke) lines should be taken out and shot. Her dialogue was totally out of place and ruined practically EVERY scene she was in. And the whole "secret" lesbian sub-plot was overplayed and un-necessary.
12) Where the fuck is everyone else in town?!?!?! There is a school full of school-children, but there is LITERALLY nobody else in town other than the main characters, the military, and the new "rich" family shoe-horned in for the plot. Other than that, this supposed town that has gone "back to normal" is a ghost-town.
13) Speaking of empty...where the fuck are all the monsters in the upside down??? Where's the mind-flayer?? Where are the flying bat-things that killed Eddie?? Where are the roaming hoards of demi-gorgons? Now, apparently there is only a couple of demigorgons that are sent out on specific missions by Vecna?? So the whole upside down is conveniently empty enough that the military can build an ENTIRE FUCKING BASE, equipped with power, buildings, water, vehicles, and fucking helicopters?!?!? GTFOOH!!
14) Finally, did they really need to bring back the other escaped patient girl from S2, Kali?? I literally completely forgot she exists, and now we are to accept that SHE is the military's secret weapon???? Ok Jan....