The structure of the book (example chapter, XPATH chapter, stylesheet chapter, reference section) is okay, but the quality of the chapters needs improving.
The chapter introducing the books example uses not so obvious xsl syntax, that is not sufficiently explained. Later chapters that explain individual xsl syntax constructs, sometimes only skip the surface. I was particularly upset by the remark "you can almost guess how the xsl:choose works" (or similar); the text didn't delve into it any further!
I feel the reference chapter contains examples that are too complex: an example supposed to explain one xsl construct, also contains a large number of other xsl constructs; you won't be able to understand the one construct if you don't already understand the other constructs. Also, the reference chapter is not very elaborate, omitting the finer details of a particular construct (e.g. multiple consecutive xsl:for elements are said to be handled "all at the same time").
For an introductory text, I find I have to browse to later chapters all the time. As a reference, it's not complete enough. For a good XSLT reference I advise to buy another book.
Note: Any quotes or names of chapters mentioned above, are likely to contain errors, because I don't have the book on me at this moment...