First up the whole Billy and Mrs. Wheeler thing was just weird and completely unnecessary. They could have done anything to get Billy on the way to somewhere at that time of night, instead of some weird cougar with a kid kind of deal.
Second, again they had the party too split up for too long
Third Erica was annoying as fuck
Fourth. I feel like the chain of events happened way too quickly. The other two seasons took place over days and a couple weeks. This one seemed to all happen within a couple of days. And even if there was more time spanning in the first half, shit just felt like it was a mad dash to the next big set piece or cheesy 80s reference.
Fifth: Part of the charm of this show to me was they truly treated it like it was being made in the 80's. Especially in the 1st season where it was almost all practical effects. I know they leaned pretty heavily on CGI in 2, but God damn, they dialed that shit to 11 in 3.
I don't know if I'm going to word this right, but here goes: This season seemed to be missing the heart the other two seasons had. The little moments between characters that made them truly come alive and feel close to you. And they kind of forgot the subtlety they had as well. They never dwelt on the 84 presidential race in season 2. They just had signs in the yards as they panned across someone's house. That's what made it feel like you were really in the 80's is they acted just like they would if they were living in the times. This season it just screamed "HEY REMEMBER BACK TO THE FUTURE???? OR GOING TO A MALL??? OR NEW COKE??? YEAH THAT SHIT WAS NASTY!" And then Steve and Dustin's chemistry was awesome in season 2, and they continued that in season 3, despite the situation being absurd even for a show about absurd shit happening. However, it felt flat for Hop and Joyce. That's not the relationship they have had, and the whole Starsky and Hutch bullshit was kind of lame to me. Murray and Smirnoff saved the day in that group.
With that said, I loved the overall story. And some of the action was legit balls to the wall and a blast to watch. The crazy Terminator/Darth Vader love child was fucking cool as hell. The ending tore my heart out. I loved Hop as I heavily identified with his relationship with El due to the similarities it shared with the relationship I have with my own daughter. Seeing El read his letter was gut wrenching. However (god I don't want to go negative here again) it will be shitty if he actually survived that explosion. I loved how El got through to Billy, and she wasn't super Dues Ex Machina for a 3rd time. The Finale was legit tits.
Robin was an awesome character. And while her big "reveal" was ok, I don't think someone fresh out of high school coming out would be as well taken in 1985 in small town Indiana. I grew up where this story is set almost to a T (Hell my home town is where Purdue is which is referenced), and I can assure you being gay was not popular at all in the 80's in smaller town Indiana. Either way she kind of stole the show for me.
The Mike and El relationship has been sweet on so many levels, but I'm afraid they are going to muck it up by introducing another love interest for El at whatever new place they live. I get it, it'd be realistic, but again 80's was over the top cheese, and I'd kind of like to keep that.