I haven't personally read it (shame on me!) David Herman and I spoke from time-to-time while I was at Mozilla and he's very smart, a very clear communicator and he knows the language as only a language lawyer can. He's actually a member of TC-39 (the ECMAScript committee) and had a big hand in the modules coming in ES6.

By every account I've seen, it's a great book and the only reason I haven't read it is that I've already been bitten by all of JS' pitfalls once or twice :)

The real reason I'm posting a comment, though, is to give you a link to the JS Jabber episode in which they talk to Dave about the book:

http://javascriptjabber.com/044-jsj-book-club-effective-java...

That episode will give you a good idea of what the book is like.