Like all L.Frank Baum books these are targeted towards children as a modern fairy tale. Which they most definitely are.
However, I’m never a fan of the plot device of sending in an omnipotent character to rescue a person in distress. It lessens the story a bit, there’s no struggle to achieve the goal.
He does do a very good job of tying off all the loose ends of the book, which make the book that much longer and possibly unnecessary, but again this is a kids book and it answers all the questions that are left hanging.
It was a fun read, (up until the omnipotent being swoops in to rescue everybody), and I will continue to read all the books in this series.