Finished the first season of Made in Abyss, and I have to say it's really good! The premise is really great, exploring an impossibly deep magical mystery hole filled with dangerous creatures and ancient treasure just can't not be good. The only problem is that the timescale since it's discovery (1900 years) strains my credulity. The monster design is excellent as well. The characters are also really good. They are all really endearing, especially Reg who, being a robot, acts with more naivete and emotion than anyone else. It's adorable seeing him get scared by being told a ghost story despite the fact that he has a disintegration cannon mounted on his arm. Nanachi, despite only being introduced in the last 4 episode has already received a huge amount of development and is quickly becoming my favorite character. Best of all, we haven't had any misunderstanding based character drama! Even when the characters conflict (like Nat and Riko near the start) it's handled in a believable way. And the characters being so likeable works fantastic for the show, because it means you really care when horrible stuff happens to them, which it does because that is what happens when a normal human child descends into a den of monsters. The scene where Reg desperately attempts to amputate Riko's arm, sobbing and making a horrible mess because he doesn't have any idea what he's doing was one of the hardest to watch scene's I've ever seen in an anime. And I'll admit, I cried during the season finale when Reg incinerated Mitty, It was an arc told in just a couple episodes, but it worked so well.
My main problem with the show is that it's just moving too fast. By the end of the 13 episodes of season 1 we've already crossed 4/7 layers of the Abyss. It's a real shame because the Abyss seems like a really interesting place, and it would have been great to explore it in a bit more detail. I get that Riko wants to reach the bottom as soon as possible, but I want to explore and see some treasure!