I love the Head First series, although this book is not for people who already live in an OO world. If you know Java and HTML, 60% of this book will be review of basic coding principles.
So, it was the wrong book for me. But it's very readable and engaging and useful as a teaching tool. It makes a poor reference (all the Head First books do), but it's not intended to be one, so we can't fault it too much for that.
It also does a good job of addressing JS's myriad weaknesses (duck-typing, lack of testability) without dwelling on them, mocking them, or apologizing for them.
So, overall, good book for someone with little coding experience who wants to get into dynamic pages without jumping straight into GWT.