I don't know the manga to this but I think the anime would be probably a nice edition AFTER you read the Manga. At least that's what it feels like.
You start with the end of the prelude and get the story told in a flashback but you have know idea what this is all about. The beginning of the Anime is actually right in the middle of the story. First it seems like a "normal student story" but then it gets more and more into the scifi aspect, which is for my taste not enough explained. For example why especially this place and what happens between the end of the flashback and the present time. Why did it take that long?
But the story itself is very interesting, especially since it's so rich with secondary characters and their story. I also like the animation a lot.

All together it is a good anime - it is not my favourite but I may watch it again some time. I just wished they'd done 24 episodes so you hadn't had to move that quickly in the end and we would have gotten more information. Like that it leaves a lot of questions unanswered. That's why the low rating. An interesting story is only good if it's played out. (show less)