I read the 6th edition and it seems that the 6th is very different from the 5th. Overall, I found this a very helpful guide for HTML, XHTML, and CSS. I liked that it incorporated actual code and then a screen shot of what the code would/should look like on your browser.
Castro only discusses simple coding, but she makes it easy to segue into the more advanced coding.
Interestingly, not all of her code was w3 compliant I think for the purpose of simplicity, but overall, I found this to be a very helpful aid.
This was the textbook for a class on HTML, CSS, and a little JavaScript that I'm finishing up. The book did a good job of serving that purpose for me. Each topic covered is broken down into only a couple of pages with illustrated examples on every page so it is easy to read about what you want efficiently. Also, the website that supplements the book and contains code for all of the examples in the book was very useful.
I borrowed this book from the public library for use during the class and to see if I thought it was worth buying for future use. While it was good for learning new stuff (especially with the online examples), I probably won't buy a copy. It is not bad for reference purposes, but I've found the online resource at w3schools.com better for that as W3Schools is more complete. To be fair to the book, I assume Castro did not intended it to be as complete as a reference book/site would be at the risk of confusing a reader who is new to the material. However, now that I am not new to the material, I prefer a more complete reference.
It was a textbook for me so really, how good could it be? While Castro's explanations and directions are clear and easy to follow, some of the techniques are already outdated. The best part of the book is actually her website where you get to see the techniques in action.