Where the book becomes more interesting is in Parts II ("Programming Practices") and III ("Automation"). Again: the chapters that comprise Part II are going to seem like review for many seasoned JS devs: keep your JS and your mark-up loosely coupled; avoid global variables; keep configuration data separate from business logic; use feature detection instead of browser detection. As much of these may seem like review (especially if you've been keeping up with Zakas' blog posts), don't get cocky and skim it, either--there are some gems in there. (In particular I'm thinking of the chapter on Event Handling that spawned an interesting post by Ben Nadel.)
The chapters in the Automation section were my favorites. Zakas builds up a solid Ant-based build system over the course of 7 chapters that includes validation and linting, file concatenation and gzipping, minification, documentation, and automated testing. As I've become highly interested in the build process, I was riveted by these chapters. Zakas at least touched on every topic in the automation/build topic that I would have wanted to see. But that being said: I would have loved to see more on this subject. He provides a lot of excellent starter material, and Appendix B is a rich list of other jumping-off points, but it also seemed... shallow? Like he was just scratching the surface? This seemed especially true of the chapters on documentation and testing.