First things first, I think the show sticks the landing. There's no flagrant last-minute swerve that confuses or confounds, the characters remain true to themselves.
My immediate point of comparison is with Game of Thrones, whose ending (the last two seasons in general, but in particular the final wrenching heel-turn for one of its core protagonists) took a wrecking ball to the good will it had built up over the previous 8 years.
Stranger Things, while it has had fewer episodes and seasons, was nevertheless "running" for even longer, nine years, and so there was a lot of pressure to live up to its expectations.
I literally finished it just a few minutes ago, so these are my raw impressions, but broadly speaking, I think the show manages to end in a satisfying way. I'll get into specifics beyond a spoiler cut.
Spoilers Ahead:
