This was my first JavaScript book and I consider it a good overview covering the pros and cons of the language. The author gives good advice regarding which features of pure JavaScript are fine to use and for which features a framework should be preferred to avoid browser incompatibilities.
Many popular applications are demonstrated (custom tooltips, infinite scrolling, form validation, autocompletion, lightbox, 3rd party APIs) and concepts such as client vs server programming are clearly explained. Christophe's focus on Prototype is not a problem for me. It's his favorite framework and the one that he knows well, so it make sense that he's using it for the demos.
One practical problem: this book is not maintained any more, and as a consequence a few examples are broken, due to a domain that has expired and changes to the Twitter API. I contacted the author on GitHub and he confirmed it. But still, for a book that was published five years ago it's a nice compact guide to people who are familiar with programming and want to focus on the specifics of JavaScript.