I had a love-hate relationship with this book. The book is sensibly put together and does indeed deliver on its promise to give a pretty complete picture of the evolution of Spanish from Latin.
Particularly interesting to me was to see how Spanish drifted from the heavily synthetic Latin toward becoming a more analytical language (i.e. in its construction of future and past tenses with "he hablado" and "hablar he") and has since become more analytic again (in modern Spanish, "he hablado" and "hablaré" can not be separated as separate words, and the enclitic pronouns have morphed from pronouns into a form of object agreement build into the verb).
However, I found that I had to provide much of the enthusiasm and interest reading the book. Although the author was not without interest in his subject matter, this was written as a text book and, though it's not formatted like one exactly, it has enough textbook in it to make it occasionally dull.
It's hard to say why exactly this should be, but I think it's in the sense that some material is inserted for "coverage" sake rather than for interest's sake. That's not to say that some of the material is uninteresting -- I think essentially everything in this book is of interest -- but that it is presented as "complete" rather than as intriguing (even though, as an introductory text, it is of course far from a complete account, as the author explains in the introduction).
So, in the end, I had a similar relationship to this book as I had to my intro linguistic anthropology course at Brown -- namely, I loved the subject matter, but was concerned that the author/professor didn't love the material as much as they should have. Which is to say, I wish the author at brought a bit more zeal to the book. That said, it is the curse of surveys of all kinds to feel shallow and inadequate. Nonetheless, I know a great deal more about the history of Spanish now, and I will certainly keep this book handy as a reference for years to come.