To say it with the authors preference for Shakespeare: Much Ado About Nothing!
The author largely fails to present motivational reasons, why a a specific feature should be used instead of alternatives. But luckily, this lack of reasoning is evened out by printing a neat JSON parser on another six pages in Appendix E. Go figure!
In most code examples, the interesting bit is obscured by useless noise, which does not contribute to an understandable explanation of the topic at hand. This is unsatisfying and disappointing, because exciting language features become a fuzzy blur.
Five stars for the idea and the attempt, and for covering a wide range of topics. Sadly, I have to pull three stars for the weak execution.