We finished our most recent in the Oz series yesterday, The Tik-Tok of Oz. I have to say that this was my least favorite of the series so far. It fits in just fine, but it borrowed heavily from previous books, to the point that I felt it was just a rewriting or a recombination of earlier stories he'd already written. That being said, all the stories are really formulaic and that might be part of what makes them so enjoyable to the younger set—they know what to expect, and they are all equally fantastical and enjoyable. Calvin, for one, was not bothered by repetition.
Since I thought the book was somewhat of a bust I think my favorite part is Calvin's journal entry. When we started with this half a year ago I was spelling everything for him and still helping him form letters and the sentence structure to get his ideas out. He wrote this entry entirely by himself while I was running on the treadmill. I am completely in love with it.