"Stranger Things" is really, really good. It might even be great.
But lets start with a more factual account. "Stranger Things" is a Netflix original series. The first season consisted of eight episodes, and was released in July of 2016. The second season, consisting of nine episodes, was released in October of 2017. The show is a horror/science fiction show, with aspects of mystery and espionage. In my view, the first season felt more like a fantasy or horror story, while the second season managed to be a harder science-fiction story. The show most famous star was Winona Ryder, and while she received top billing, the story is not mostly about her. The show was very successful, and critically well-received, and contributed several pieces of cultural currency, such as the Christmas Lights scene.
One of the most noticeable things about the show is that it is set in the 1980s. The first season is set in 1983, and the second in 1984. The costumes, cars, technology, haircuts, decor, attitudes, everything, are almost perfectly done. Someone with a very fine toothed comb could look over the show and find a few anachronisms that snuck in, but in general, the show functions as a perfect period piece. Certain aspects of the plot are only possible because of the 1980s setting.
The plot of Stranger Things begins with a group of preteen friends playing a game of Dungeons & Dragons, and then bicycling home in their small Indiana town. On the way back, one of them, Will Byers, hears something in the wood and starts to run...and then disappears. The next day, he still isn't home. Despite the fact that it is 1983 and children are still free range, this alarms his mother, Joyce Byers (played by Winona Ryder) and she calls the local police chief, Jim Hopper, for help. Despite his seemingly lazy and rough demeanor, Jim Hopper begins to believe that the mystery behind Will's disappearance might be more than it seems. Will's three friends also want to find their lost friend, and when a strange girl with a shaved head and unusual speech shows up, they think they might have a lead that none of the adults in the town have. And incidentally, this town has a mysterious Department of Energy research lab on the outskirts of town...before long, the mystery is being described from three intersecting angles: the band of preteen children, their older, teenage siblings, and the adults, all investigating at cross-purposes. Along with the science-fiction story, the young people in the story also undergo a coming of age story.
Describing it, none of this is a particularly original story. As many people have pointed out, the story borrows heavily from 80s cinema: The Goonies, It, E.T., Alien and Aliens, Altered States, Fire Starter---in many ways, this is a combination of some stock plots: the Ragtag Group of Misfits, the simple country sheriff who isn't as simple as he seems, the heartless and secretive scientists, among many others. The execution of it is done superbly, and the shifts in tone between the mundane and the paranormal are done seamlessly.
Everyone who is a fan of this show will probably have a different reason for liking it. For me, the appeal is how perfectly it recreates its period. Although I am a little younger than the characters in the show, the childhood depicted in Stranger Things is not that different from my own. Which makes the horror and mystery more believable and immersive for me: because I did go into the woods and get scared and see things, and then wander back out into a world of cul-de-sacs where kids would discuss Dungeons & Dragons at our neighborhood meeting place. For me, the appeal of "Stranger Things" is how it presents the liminal nature of things behind the everyday world, and how it subtly connects the idea of supernatural evil with the cruelty and callousness of everyday life. Although I appreciate the series building up an involved and detailed cosmology, it is the earlier episodes, where we can't be sure what is normal, what is madness, and what is conspiracy and misdirection, that gave me the greatest feeling of horror.
In my first sentence, I said that Stranger Things was very good, but I don't yet know if it is great. There are more seasons to come, we hope, of "Stranger Things", and more directions for it to take. Right now, it is unclear whether it will be seen as just a very well executed example of the horror genre, or whether it will be seen as a definitive, innovative work in its own right. At this point, I wouldn't bet against it.