I think the showrunners were trying to turn the "kid sibling" trope on its ear by having Erica be more aware than the cutesy kids one would see in Spielberg films (or ripoffs of his films). I found her continued use of "Child endangerment" funny, because she's not only calling out the others on the mission, but speaking for the audience who should naturally think, "She's a child! Are you really going to send her into a secretive place with armed guards?"
Eh, for me it was too much. I mean there's already a
lot we have to accept for this story to work and the entire genre it's playing in. We don't need a character peaking over the fourth wall saying things like this, I mean in this genre we have to accept that bunch of kids can just penetrate a Russian base and pretty much not get caught until things really go wrong. We don't need this character playing a precocious role and doing the smug tropes of "I have something you want, but you need to give me something first so I'm going to continue to turn down a progressing series of offers until I smugly demand you give me everything. It was just too much and it never reached a point where it was "endearing" or even entertaining.
I think Mike is an asshole little kid who was clearly not smacked by his parents enough and he lives in the 19-fucking--80s. Somehow Nancy turned out "normal" but, he's a little asshole. Constantly yelling at his parents when they do things like call him up for a meal or something, and the disrespectful way he behaved towards Hopper, whispering things at Eleven when Hopper sat them down for the "heart to heart."
Yeah, yeah, he's a young teenager and all of that, I get it. But the kid is an asshole.
But, he's a... "fun" asshole. He's played well and fits into everything and his group of friends.
(I speak of the character, not the actor Finn Wolfhard who does a good job, and in other stuff he's done.)
Erica was just annoying, she was already too much to take with her abusing the free-sample policy at the ice cream shop then she gets chucked into the main story. I mean, why have Dusty meet-up with the others and have these characters be together in this story when we can chuck in this new annoying character?
Anyway, after thinking it over, I think I might rate this season higher than S2, there were some aspects of it that worked better and just some more interesting elements.
Just not Erica or the scene with Dusty and the girl in Utah singing over the radio during a tense moment. That was also a bit... Dumb in the context of the scene, what was going on, and how it contributed to Hopper's apparent death.