This is a great book, since it not so much treats the basics of programming (as do many other MINDSTORMS books) but pays equally balanced attention to the principles behind making good mechanical constructions. I especially like the places where behaviorial issues that are seemingly 'obviously programming' are obtained by clever mechanical solutions, since it matches my own way of looking at MINDSTORMS. Often, these solutions free up motor and sensor ports, and therefore permit to add more behavior onto the basic behavior of the original design.
You really learn many things from this book which you do not find in other MINDSTORMS books, because the authors take a pleasantly fundamental approach. There are chapters on LEGO geometry, and a chapter on walking robots starts with an experimental explanation of the center-of-gravity, which is of course the fundamental problem behind the designs that follow. There are also some basics of signal processing which should help solve sensory issues structurally, without hacking, another commendable improvement over comparable books that ignore such problems.
The playfulness of the authors shines throughout, and this is what makes this serious book such inspirational fun - who would think of using MINDSTORMS to build a pinball machine or flight simulator? It is brimming with non-traditional ideas like these. The many illustrations are excellent, and there is enjoyment at every level: the design issues at large (such as what to relegate to the hardware, and what to the software), but also the design details; for instance there is an incredibly compact and simple turtle foot that needs to be built to be believed.
Beyond the fun, the book really serves as a good introduction to the principles of robotics, with LEGO as the tangible and affordable illustration of those principles. Useful tables in appendices convey the new flavor: MINDSTORMS is now being elevated from a toy to a specific technical design platform, and thus professionalized (to the extent that the tool allows, of course). In my mind, this enhances rather than reduces the enjoyment of the kits, since the structural approach should eliminate many minor frustrations in designing working robots.