This book presents an excellent overview of interior-rotor brushless motor design. I tend to prefer textbooks that aim to build intuition over cookbook-style handbooks or excessively-mathematical formulations. Math is a language to express physical reality, some books act like math itself constitutes that reality.
Hence, this book's strength is its simplicity. Starting from the basics - short and open magnetic circuits with a single permanent magnet, then on to the simple case of a single wire moving through a field - Hanselman builds up to a full discussion of pole and tooth count, dimensions, and windings. He discusses tradeoffs inherent in design, and how to maximize efficiency. The one area I think could use a little elaboration in a future edition would be the section on motor constant (torque / losses), and a distillation of the design rules in one place. Right now there are useful nuggets scattered around the book, combining them all in one section at the end would help.
So, not the most comprehensive or the most mathematically rigorous, but extremely helpful for building intuition.