I only get the complaints looking at it as something that took the audience away from the story in Hawkins. I get wanting to get to the end. I get being annoyed by the seeming disruption of the flow of the story. But it didn't bother me at all. For one there's A LOT of stories told with that kind of flow. Secondly it built up anticipation of the last two chapters. As for the complaint about content... They baffle me as well. I don't think the actors themselves were at all bad by any reasonable standard. If they weren't the cute and cuddly, likable cast we've grown to love back in Hawkins... THAT WAS THE POINT. You weren't supposed to like this group. And if the general vibe of the urban scene seemed to clash with the rural/suburban tone of sweet nostalgia built up over all the previous episodes going back to season one? Once again, that was the point. Hawkins and boys are but a slice of America in 1983/1984. For many the world shown in the scenes with 8 were a hell of a lot closer to what that period felt like. We tend to view the 1980's through the haze of the "optimistic" Reagan presidency but what we really mean is Reagan's SECOND term. From 80-late 84 there was still a sort of 70's hangover happening for much of the country. Let's put it this way... Punk gives way to New Wave for a reason.
Now when it comes to the content of the episode... I STILL DON'T GET THE HUBUB.
The episode expanded the mythology of the show beyond simply the fight against the Upside Down, gave texture and back story to the experiments at Hawkins that led to 11, teased stories for future seasons, gave 11 a taste of what her life could have been away from the good influences of the boys, Hopper and Joyce, and yeah... If you were a fan of X-Men comics, this obviously took influence from that period of the Mutants when Claremont was at the height of his powers. I mean... I thought the nostalgic references were part of the show's appeal?
And more than the "vibe" 11's bittersweet discovery of more young people like her indeed showed the line between her journey of self discovery and 8's need to lash out at the world for wronging her regardless of consequences, moral or practical. This was classic Xavier/Magneto stuff. The clash between someone that wants to be integrated into the world and someone that believes in "by any means necessary".
I am not asking anyone to love the episode, but as with a lot of online "debate" there seems to be no real nuance in criticizing this particular little side story that I dare say will be very consequential going forward, not to mention another showing of internet group think in condemning the target du jour.