NO SPOILERS
Story(8) I think Kiseijuu has a good story, a bit too simple sometimes(some events are too predictables). Despite this, from the beginning to the ending, I really enjoyed this anime. There is a simple philosophical thought all along the episodes but it led us to think about it very deeply.
Art(8) The line is clean like the colors, the animation is fluid. The negative point is the some battles scenes where the animation is a bit simplified but it won't really affect your enjoyment.
Sound(7) I liked the opening, the ending and "Next to you" but I don't really appreciate the dubsteps musics which are in Kiseijuu. I fancy it doesn't fit with the atmosphere.
Character(8) It's pleasant to see the evolution of Migi and Izumi nevertheless, some characters aren't enough developed in my mind.
Enjoyment and Overall(9) Kiseijuu is a very good experience, very enjoyable where we rapidly get into a real thinking despite the little defects. I recommend it!