I gave the first edition of this book five stars, because it really has been the first and most definitive book on the subject. That edition had some quality and editing problems, but these have been addressed in the second edition. Indeed many of the explanations have been much improved.
As a means for learning the semantic web, this is perfect.
Having previously read it and more or less understood the topic as a whole, however, a year later I am trying to solve a problem and I need a reference book. In this role, it is seriously lacking. The index is terrible. There is no glossary. I tried to look up "objectProperty" and "dataTypeProperty" (to me, the most important "properties"). Indeed, I tried to figure out exactly what the authors' definition of "property" is. "Equivalent", "intersection", "transfer", and "union" are indexed under "property", but the basic definition of the word is not to be found, nor are the two main kinds of properties I just referred to. I wanted to figure out the difference between "type" and "class". I did eventually, but neither term shows up in the index. (OK, "class" does, with 10 sub-terms, but none of them include the basic definition of the word.) What is the difference between an "rdfs:class" and an "owl:class"?
The style is as a narrative, and this is a good way to teach. As a source to answer questions, however, it is seriously lacking. Instead of "FAQ" at the end, a glossary would have been nice.