It's a weird, arty philosophical debate on the meaning of reality, social issues and how people are generally a bit shit. (As is God. He's here and he's more than a bit dodgy.) It stars a bunch of immortal but apathetic schoolkids with random superpowers who can sometimes travel between different worlds, each with their own peculiar laws of physics.
It's a fascinating universe to glimpse and dip your toe into. Misaki and Natsuki enjoyed what little they saw of the series, with visuals that sometimes made them laugh aloud. It's got worlds of baseball-playing monkeys, whimsical gravity, imposed capitalism and more. These time-adrift students have some fantastically wacky planes of reality to explore, all presented in a humourless, po-faced style that's doing it all as an existentialist treatise on the meaning of life. Some of them will be there for hundreds or even thousands of years. Since nothing can kill them, it might even be eternal. Is it heaven? Or hell? Or are they both there, somewhere? Maybe someone should have asked God? "Life is an endless exercise in vain effort."
It's also pretty boring.
My problem with the show, really, is the mostly apathetic characters. Some of them have a bit of get-up-and-go, but most of them are in a hurry to find a scapegoat on whom they can blame everything, or follow a self-proclaimed messiah, or just be shitty and stupid for no reason. I lost patience with them and didn't care what happened to them, partly because they didn't seem to either. They'll moan and whinge, but not actually do anything for themselves, beyond bleating like sheep and/or following bad orders because that's the limit of their resourcefulness.
Nagara is bored with the world(s) around him and uninterested in other people. He doesn't seem to care about anything. Blame him for something he didn't do and he'll probably just apologise without even trying to defend himself. He's also the show's main character.
Mizuho's abrasive, but can be recruited as an ally and has a brilliant superpower. She can order anything on "Nyamazon" by placing an order with her cats. This power isn't without its limitations, but these don't include "a castle is too big to fit in an Amazon cardboard box".
Nozomi's actually likeable. (She doesn't follow the herd, albeit in a cheerful way, and throws away her mobile phone.) Rajdhani's the one who loves figuring out everything and unpicking the rules of these worlds. That's almost it for people you'd rescue from a burning building, though.
For me, this isn't a story. Dramatic narratives have people making choices to achieve goals. This series, in contrast, is an essentially static examination of how people can vanish up their own arseholes, sign up for centuries to something dreary and meaningless and/or blame their lives on someone who clearly couldn't have done what they're accusing him of. There are some genuinely thoughtful episodes here, mind you, even if the show's final punchline essentially boils down to "he was a gigantic twat". It's saying some bleak, pessimistic things about people and the universe in general. It's talking about people's relationships with rules, either social or magical. It has living symbols of freedom (cats, birds, etc.) and people who may or may not lift a finger to help these. It has a lot to say about capitalism, the societies we create and the way we can dedicate ourselves to physical things (e.g. initially Mizuho).
The show's playing intellectual games. It's tying time, logic and causality into pretzels, then seeing how its characters react to all that. It is, though, a static anti-story about mostly uninteresting people.