I've already read most of the blog posts that make up the bulk of this book, but I'll still be buying the book to support Axel's work, and you should too. You won't be disappointed.
If you care about Javascript at all, this is a definite insta-buy.
Axel is one of those rare people who combine a truly deep knowledge about tech stuff with the ability to speak and write about it in a way that's accessible and at the right level of abstraction.
Considering how many ppl that now use mobile phones to surf the world wide web and that mobile phone's usually don't auto-upgrade their browser, and that we still need to polyfill ES5 features, I wonder how many years it will take until ES6 can be safely used without first "compiling" it to the ES5 standard.
I find this rather convenient - it strengthens the argument for considering languages other than ES6 that also compile to ES5 (Clojure, Scala, PureScript, TypeScript, etc).