This is basically all that happens: (SPOILER WARNING)
A bunch of people decide that time travel is bad because a bunch of people got killed because of time travel. There's also the classic time travel rule where you can't change anything with time travel because every change you make has already been made. Jonas tries to stop his dad from killing himself, then gets his dad to kill himself. The moment Adam told Jonas to do this it was painfully obvious that this was going to happen. But for some reason Jonas and the rest of the characters never catch on to this rule and proceed to kill others to try to stop time travel from being invented... by time traveling. You'd think Jonas would have caught on after his entire lifetime of time travel. Why on Earth does Adam think that destroying Martha and the origin would put an end to everything despite this basic rule? There's no reason to care about what anyone does because you know how it ends, only laugh at how stupid they are despite all their plotting and scheming.
So with Adam failing to stop time travel after killing Martha (obviously wouldn't work), in that moment everything leading up to the second to last episode meant nothing. Then in the very last episode Claudia just randomly shows up and is just like: "Here's how to stop time travel: Just travel back in time and stop time travel from being invented lol. Didn't work the other times it's been tried, but it'll work now" And then it works because of some random loophole. That's the entire show
I thought the dialogue was often corny, "Time is God, we're waging war against God." "The wormhole in the power plant is God." Many obnoxious, forced biblical references. Not to mention the condescending voice overs explaining things like Schrodinger's Cat and the whole "Time is not a line but a circle" spiel we've heard in many time travel stories. There's like a dozen voiceovers repeating the idea of "the endless cycle" over and over again.
I believe the creators stated in an interview that they were considering basing what happens in future seasons on fan theories, meaning that they didn't have the whole series planned out much and were making it up on a season-to-season basis. It would explain why Mikkel committed suicide for such a stupid reason or why they never gave any reason for why Jonas became Adam, they hadn't planned it yet when they decided to start the series with his suicide or when it was revealed that Adam was Jonas. I was really curious what developments would happen that would shape Jonas to becoming Adam, but it just sort of happens, apparently.
Though it wasn't all bad, the vibe, cinematography, acting, and some of the drama was good. I do remember being somewhat captivated by the mystery in the earlier part of the show.