I don't find the trailer particularly inspiring. There's some interesting stuff there, but also some bits that look stupid or out-of-place. (Playing electric guitar in the Upside-Down?)
I thought Season 3 was no-where near as good as the first two. (Pretty much everything you said Thales!)
After missing a Russian base under the town, how does anyone in the US know what's happening in Russia? Will the two locations be separate until the kids go from one place through the Upside-Down and emerge in Russia by accident, or something?

I really hope they have a better set-up and story this time round. At least by expecting to be dissapointed, I might be pleasantly surprised!