What really blows my mind is the sheer amount of worldbuilding involved, as seen in the end pages for the first several chapters (although not so much in later ones, sadly). Thinking about how the evolution worked, the whole six-limbs thing, Antarctican society and biology, the various religions/myths, the little bits of history that are hinted at, etc. It all makes this something special, and far deeper than the slice of life format would suggest.
That, and adorable little centaur children and class rep's sisters.