The authors do a very good job of laying out their topics, and I enjoyed their clear, enjoyable writing style. I think they do a pretty good job of discussing good development, and they're all over things like browser compatibility issues and other "Gotcha!" type issues. They've got a nice set of sidebars for tricks and tips as well as things to look out for.
I also like that it's another SitePoint book with loads of color throughout. I'm not sure how SitePoint does it, but their continuing journey with all the color books is absolutely great to behold.
On the downside, I'm not a fan of some of the example code I saw, which in several cases was more convoluted than good design would dictate (multiple nested for loops, return statements from other method calls being used as return values themselves, etc.). I also would have liked to see some discussion of testing via tools like Selenium or JsUnit.
That said, overall I like the book a lot. They talk standards, they talk cool tools like FireBug, they make some headway with good decisions about separation of code, content, and style.
I'm almost done with the book and have been very happy with its content.