A useful, if imperfect, resource for students and teachers of Koine Greek
If you are an intermediate or advanced student of New Testament (Koine) Greek, or especially if you are a teacher of NT Greek, then this book is definitely worth having in your personal library. I wouldn't recommend it for beginning students, since it presupposes that the reader is familiar with the basics of the language; but once you've mastered the fundamentals, this book can certainly add something of value to your understanding of Koine Greek.
However, the book has at least a few major flaws which prevent me from giving it a wholehearted "five star" recommendation. These flaws are mainly due to when this book was published—at least some of the information it contains is outdated, since both the field of linguistics and the field of Koine Greek studies have evolved quite a bit over the past two decades. The main problems come in the chapter on phonetics. There are two major problems: First, the terminology that the author uses for describing the sounds of spoken Greek is a bit out of date—the terms that linguists now prefer to use for describing these sounds are at least slightly different from those used in this book. It's not that the author is wrong—the terms that he uses were in vogue at one time—it's just that the terminology used in any field of study will tend to change over time, and so a book that is more than 20 years old will almost certainly include at least some outdated terms. This is not a problem if you don't care about how up-to-date the terminology is, but you at least need to know that the way the author describes certain speech sounds is not the way that most linguists would describe those sounds today.
The second major problem in the chapter on phonetics—and the more important of the two, at least in my opinion—is the author's uncritical use of the traditional Erasmian pronunciation, which we now know to be entirely artificial. Originally devised in the early 16th century by the scholar Desiderius Erasmus, and tweaked in various ways over the following centuries, this method of pronouncing Ancient Greek does not accurately reflect how the language actually sounded at any single point in its history. It uses some of the sounds of Classical (Attic) Greek—i.e. the Greek of Plato and Aristotle—and some of the sounds of Koine Greek, but a time traveler who knew only the Erasmian pronunciation would have difficulty making himself understood by Greek speakers in 5th century BC Athens, 2nd century BC Alexandria, or 1st century AD Antioch. I'm not really sure exactly when scholars first became aware that the Erasmian pronunciation was flawed or when they first reconstructed how the ancient language was actually pronounced at various points in its history, so I don't want to fault the author too much here—when he wrote the book in the mid-1990s, the problems with the Erasmian pronunciation might not have been well understood, and more authentic pronunciation schemes might not have yet become available. Nonetheless, his chapter on phonetics makes no mention of the fact that the pronunciation system he uses is artificial, nor does it mention the existence of alternative methods of pronunciation. It simply presents the Erasmian pronunciation as if that is how Koine Greek actually sounded when the New Testament was written. Because this error has such a powerful potential to mislead students, I am unable to give this book a "five star" recommendation.