I'm not generally a fan of time-travel stories. They seem to follow the Terminator and Back to the Future patterns, in which someone travels into the past in order to make something happen or not happen in order to change something in the future, and that usually turns into a fairly straightforward adventure or comedy. But this one is richer and more fascinating than most, at least within my not-all-that-extensive experience. That usual pattern does become a factor but I think not until fairly near the end of the first 10-episode series. There is a whole lot more going on.
There are two seasons, and I've recently finished the first. It doesn't by any means end the story, and I'm a little concerned that the second will not do that, either, as a third (at least) is planned. But I'm definitely going to watch it.
Season one, at any rate, involves three points in a 66-year span: 1953, 1986, 2019. That's a 33-year interval, constituting a cycle in which the lunar and solar years are somehow in sync. I'm sorry, but I have not bothered to understand exactly how this works, and it probably doesn't matter. For purposes of the show's mythos, I think it's enough to know that this cycle has cosmic significance.
The story begins in 2019 and involves, mainly, four families in a small German town. They are connected in complex ways in 2019, and as things develop we see that they have been connected for a long time. There is a constant interweaving of times and characters, of past and present. I'm not even going to attempt an overview. I haven't counted but among four families there must be several dozen people involved, and their interactions are complex even without the added confusion of people moving around in time.
Moreover, what's going on--the time-travel stuff and various related matters--is conceptually complex (and of course includes some pseudo-scientific mumbo-jumbo which probably doesn't actually make sense). You may find it easier than I did, or more difficult, but for me it became exasperatingly hard to follow at times. But it was also interesting enough that I re-watched parts of it, just to try to understand what was happening.
It's also appropriately named: it's very dark. It's not really explicitly violent, but it involves the deaths of several children, and although their murders are not depicted, their bodies, with horrible injuries to their faces, are shown repeatedly. Also--this is pretty minor, but worth mentioning: the opening includes a brief but pretty explicit sex scene which has absolutely no artistic reason for being so. This is an annoying thing which I've noticed in several shows, which tells me that it's not an accident: start things off with a single attention-grabbing sex scene, and after that just tend to the story and don't do it again. Seems pretty cynical.
It is extremely well-done, and as I say I'm finding it fascinating. So this is a recommendation, but a qualified one, due to the dark subject matter and the complexity. (And yeah I know some people can't deal with subtitles.) This trailer will give you a pretty good feel for it, though it doesn't provide any very definite information. Many of the moments included here are not actually very important to the story. The trailer also allows you to hear part of the gorgeous and extremely appropriate song from the opening titles, which is the work of the German musician Apparat.
Apparently a lot of people are comparing it to Stranger Things, but I don't think that's especially accurate. I think that's probably just because a significant part of it occurs in 1986, providing plenty of opportunity for depicting '80s pop culture and fashion.