I don't rate children's books because any comparisons with the usual things I read would be meaningless. I read it to my daughter (seven years old) over several night's bedtimes. I had read it myself when I was a child but I couldn't really remember any of it, although I remember being fascinated with the idea of living on a tiny little planet like that.
There was an array of not so subtle metaphores in there around a strange little story with a bitter sweet, ambiguous ending. I can only judge it by my daughter's reaction to the story, who seemed to enjoy it although her attention did stray at times. The narrative would sometimes wander off on incidental tangents that I think someone so young wouldn't really appreciate. She did find some of the characters the prince met on his journey quite funny, especially the king who thought he was the ruler of the entire universe. She did comment at the end on the fact that there were no female characters in the story.
Not a bad childrens book that is at least quite different from anything else they are likely to read.