To be honest, up until about the 20th or so episode I was still apprehensive about this show. It was interesting, but it didn't really grab me that much. However, after finishing this show I can say with certainty that only a creative genius could have come up with this story.
The music in this show was really good, but not amazing. I actually noticed it at times, and usually I don't ever notice the music when I watch a show, it just adds to whatever mood it is playing over. The animation I didn't really like, honestly. The backgrounds and stationary objects were obviously done by people who cared, but the actual people and creatures that moved around felt a little flat. That may be because of when it came out, but I don't really think so. There were a few episodes towards the beginning that had weirdly poor animation, but other than that it was mostly the same all the way through.
The story is by far this show's strongest point. There are some slow parts, there are some weird parts, but the culmination of all this after you've finished the show is where it really shines. Looking back, there aren't any plot holes or anything that doesn't make sense, and everything I can remember fits in with the story well, no matter how weird it is. At the start, everything is confusing and you have no idea what is going on, but the more you progress into the story the more things are explained and the more you find out. In my opinion, this way of giving people info about the world is really satisfying. The ending is also well done, as it is with every great story. It was a little weird watching them grow up at an irregular rate, but the coming of age style of storytelling does fit what is going on well.
It might be weird to mention this, but I don't want anyone turned off by this: there is a gay kiss in the show. First of all, there's nothing wrong with that and it does nothing to impact the integrity or ingenuity of the story, and second, there are also a few yuri kisses in there as well ;). That part of the story only really goes on for one episode, it's explained why it happened, and the mystery and interest comes back at the end of that episode.
Also something that might turn people off; this show is pretty dark and does not shy away from gore, death, or violence. It's not the darkest show in the world, but if you only watch moe shows (which is basically me, but I like other stuff too) or you are really young (10 or under) you might not want to watch it. Also, if like being told everything directly rather than actually thinking and being trusted to figure stuff out yourself, maybe don't watch it.
Overall, I think I would recommend this anime. It is a very unique show with an amazing story that is good if you want something different than your typical slice drama, comedy, or action anime.
