Proper (& sufficient) description of the recent changes in ES (2016 & 2017). Nothing more & nothing less. In fact, the majority of changes is rather trivial, the biggest part of the book is all about async/await - which is by far the most complex (& challenging) change forthcoming. Description is good enough, there's a nice comparison to the promise model in place as well. To be honest, everything you find in this book can be easily found on the web, in plenty of tutorials / blog posts of comparable quality.
This little book not only introduce new APIs available since ES2016, but also give readers the reasons why they are introduced and the pitfalls the developers may meet. Great book for ES2015 users.