Everything, from the retro-style of the production, the smart casting choices (Winona Ryder is fantastic), to the intriguing "Demigorgon" monster works so well. The Duffer Brothers (Matt and Ross Duffer) deserve credit for much of this, having woven together the spectral and mundane elements of the story with confidence and style.
It helps that the nostalgia this show mines is congruent to my own experiences as a child of the mid-80s. Without being annoying about it, the show hits all of the right notes - from the awesomely boxy cars, to the amazement shown a 22-inch television screen and a Laz-E-Boy, to the inspired soundtrack choices. This feels like the 80s.
Better yet, this retro setting doesn't feel like a gratuitous move. The story Stranger Things tells (and here's where I should mention I'm only half way through the series) is one that deftly weaves elements of small town troubles, government conspiracies, and the naive optimism of middle school aged kids. It's been a long time since Hollywood has figured out how to get all of these elements together at once without it seeming campy or dismissive. Stranger Things manages that trick.
I'll finish by pointing out the monster of the series is really cool. There hasn't been that much explanation of it yet, but what appears on the screen owes something to Poltergeist, Alien, and Stephen King's IT. The Duffers are adept at using the medium of the small screen to their advantage - always locating the menace just off screen or framed at a distance through obstruction. We think we see more than we actually do, our terrified brains already supplying fangs and claws to a tiger we only hear growling.
If you have a spare second in-between binging on the show above, you might want to check out my serial web fiction, "Agent Shield and Spaceman." The twelfth chapter is now available; the agents of Section Starfire traveling to Waco, Texas to track down a lead on the source of the Burmese Tiger Snake.