I've been doing web development for the last four years, not exceptionally long, but in that time I've thrown myself into the problem space trying to become proficient. Had I read this book three years ago, I'd probably feel a lot more positive about it. Which is unfair, it's actually an excellent book, even with it's near constant referrals to the companion website, and even having finished the book, I have used it for reference on a few things that I knew I'd remembered reading in it, particularly when investigating how to deal with the IE menace from time to time.
This book is not the canonical source for any one topic, but as an overview, it's excellent. And Henick is always there pointing toward more complete resources, from references to dozens of other books or websites that cover the topics in more details. If I managed new web developers, this is probably the book I'd issue to all my hires. It contains plenty of good information, and it's a solid overview.
If you're new to the web, it's where I'd suggest you start. If you've been in the ecosystem for a while, and have really been immersed in it, well...this probably isn't the book for you. I suspect the primary reason I reached to it for reference recently was largely that it was fresh in my mind. Make no doubt, this book is useful, but the size of the problem it's talking about is so broad, that is mostly only scratches the surface. I know that I've collected more complete references on many of these issues, either in books or in links.
The book was good, but I don't necessarily think it was good for me.