Just finished it. Man, did I hate those first 3 episodes.
It really picks up after 3 though. But, I still felt the whole Russians thing was too hackneyed for the show. You always had the upside down and the monsters it created. But, now instead of a more gritty, realistic government abducting people to conduct experiments you have an absurd Russian story. Seriously, it was right out of Wet Hot American Summer. And I like WHAS, but I didn't want to see it mixed with Stranger Things.
Also, I get they wanted a realistic portrayal of teens. But, they've made me hate most of them. Mike, El, Max, and Lucas all now either annoy me or I dislike them.
The constant bickering between Joyce and Hopper got old after one episode, but the strung it out for 8.
Overall, the last 5 episodes and Steve, Dustin and Robin saved it. But, they really need to drop a ton of the teen drama and slapstick comedy for season 4.