The extended puns this book is based on are pretty clever, and Neuscwander uses them well. The narrative thread in this installment is pretty thin, however, and seems to be little more than an excuse to trot readers around to various points on the X and Y 'axes'. But then that's in keeping with the series. These books are really more about demonstrating math concepts with a narrative coating than they are about intertwining narrative and math concepts. That is, if you weren't considering teaching cartesian plotting, not much reason to read the book. Not unlike Abbott's [b:Flatland: A Romance of Many Dimensions|433567|Flatland A Romance of Many Dimensions|Edwin A. Abbott|http://d202m5krfqbpi5.cloudfront.net/books/1328868256s/433567.jpg|4243538] that way.
Wayne Geehan's illustration's are a key strength in this series. He has a painterly sensibility for color and texture, but also a very good sense for narrative composition.