The OA is original, Stranger Things is all homage.
As mentioned above, a big part of Stranger Things success is the fact that it plays to our nostalgia. The 1980s are really big right now. We are living in historic times. One might always be able to say that, but, not since I've been alive, have things been so divisive and yet so hopeful. Stranger Things has a little bit of this. However, it is ultimately a compendium of sci-fi tales from the 1980s. They have been glossed up, done with style and grace, but people watched the show because they love how they are reminded of Spielberg, The Goonies and those creepy sci-fi movies like CHUD. The OA doesn't rely on any of that. It is truly a show from and for the new millennium. The OA is always looking forward. Zal Batmanglij seems to have gone out his way to make this one of The OA's core points. Even though a lot of the show is spent looking back (in a tribal way that recalls the ancient ritual of sitting around a fire telling stories), we are always wondering where it is going? Who are these characters like Khatun? Why is the OA eating a bird of energy in her dream? Is it even a dream? The OA is really pushing itself and viewers to accept new storytelling. Sure, the grand theme idea, the stories of myth and the hero's journey are in The OA. They just are being done in a way that hasn't ever been seen before. Themes, ideas and tropes are being created specifically for this show.
The OA isn't as contained as Stranger Things.
Set in Hawkins, Indiana, Stranger Things is tied to this place in the way that the stories of Twin Peaks are tied to that fictional town. This isn't a problem. Stranger Things works so well because of it's anchor in this familiar looking milieu. The OA takes place on earth and, at the same time, it takes place in multidimensional arenas, and from there it even seems to hang its hat in the afterlife. Part of the great fun is wondering where Brit Marling's character of Prairie/The OA will end up next. All of this is amazing, special, and not like nothing we have ever seen before on TV. For Stranger Things, being contained isn't a problem for the story of each season. However, one can only wonder how many seasons it will be able to call Hawkins home? For The OA, the possibilities of where this show could go are literally limitless. There were times in this first season that I was wondering where the show might land. There is a freshness to The OA. It is almost like the show is saying that anything can and will happen. Now, unlike Stranger Things, The OA requires several leaps of faith. Ultimately, this is probably why Stranger Things will be better received. The show, while tipping its hat to Twin Peaks, is ultimately extremely accessible in a way that David Lynch's masterpiece was not. The OA is better in this regard because the story of The OA, while in some ways small and contained, is told with little regard for why space and time matter. Zal Batmanglij seems intent on showing us that we are only bound by the here and now if we believe we are.