(It's been over a month since S3 aired, so possible spoilers implicit, certainly for the first two seasons.)
The setting certainly isn't particularly unique, a mashup of familiar horror and urban fantasy tropes. (The psionic children imprisoned and experimented upon is a prime example of the latter.) The broad strokes are well-worn enough that even I, who doesn't read or even watch horror, recognize them. Some of the small details are rather clever and intriguing, especially in the visual design arena. I was charmed by the life cycle of the baby demogorgon in S2.
I'm not even that charmed by the '80s setting. I think I'm just a bit too young to really remember much of it, and since I was homeschooled, I didn't have a lot of the context the central characters do, anyhow. (Though there are a few things that I recognize here and there.) What I do appreciate as a worldbuilder, however, is how immersive this setting is. It bolsters and strengthens the supernatural aspects.
As an aside, I was pretty shocked by the newspaper office in S3. Wait, are you sure this isn't the '50s?
The strength of Stranger Things is the characters, taking familiar stereotypes - the king of high school, the prim older sister, the obnoxious journalist - and turning them on their ear. Each of these stereotypes has a stereotypical arc, an expected direction, and it's very satisfying to see them turn over, revealing another side. The reveal about Robin near the end of the season is another great example.
It's that subversion of the expected character which makes the standard setting so effective. Introduce an unfamiliar or unexpected setting, character and plot all at once, and the viewer / reader becomes unmoored. There is no context, nothing to compare and contrast. We all need some grounding in the familiar to appreciate the unfamiliar.
I also appreciate that the series has been able to build genuine suspense without knocking off main characters. (Game of Thrones, I'm looking at you.) This is probably much to account for by the decisions in the first season: if you watched it without any spoilers, you spent most of the season guessing about Will, and they made the good choice *not* to let Barbara off the hook. If she had come back, we wouldn't have trusted any death. Not even a certain one in this most recent season ...
