(Probably spoiler free)
It is great, basically. Eight not too long episodes, terrifically entertaining. The first couple of them are a bit slow, but soon after the pace picks up and things move along quite well. (Perhaps the last episode meanders a bit, but it feels earned somehow).
Much improved over ST2, which was such a disappointment in terms of expectations and potential.
The cast is terrific and the characters are so endearing. Even Billy was not-awful this time.
I have one complain: the whole idea of the Upside Down remains very vague and unexplored. There is a Lovecraftian scale to it which could be explored far beyond than its well know capacity to produce creepy monsters.
I am curious to see what will be of Season 4, whenever it shows up.