I'm a phonetics instructor, and I used this book as a sort of personal in-service training course during a break between semesters. I have been through many similar books, so much of the material was familiar, but there was also a great deal that was fresh and new for me. The book touches on some acoustic, auditory and physiological issues, but its main thrust is articulatory phonetics. It includes many excellent line drawings of the vocal tract.
The book gets off to something of a slow start, since there is a lot of background material somewhat peripheral to phonetics itself in the first three chapters, comprising part I. The main topics covered are semiotics, the different levels of speech production, and accent and dialect. It is all useful, but it left me anxious to get to the meat of the book.
Laver's use of Pike's 'contoid' and 'vocoid' categories sounded a bit sci-fi to me, but it's good to see familiar concepts analyzed in a somewhat different way. Laver will often spend time citing examples of unusual sounds, e.g. linguo-labials, where other books either omit or gloss over them quickly. The index of languages (Appendix II), is very helpful in putting into context some of the more exotic languages the examples come from. I especially appreciated the section on pulmonic ingressives (p. 168-170) since I had observed examples of these myself in northern German. I hadn't heard about their use in the Formosan language Tsou before, though I live in Taiwan.
Coarticulatory phenomena receive quite thorough treatment. The book also features a substantial section on prosody, an area that some other works tend to be weak in, and included in-depth examinations and discussions of duration, pitch, loudness, stress, and rate of speech.
The content, organization, and writing of this book are impeccable, and always clear. The only one slight drawback I found is the book's rigorous academic style, which is mainly a strength, but it can make for rather dry reading. Chapter 8, 'Stop articulations', and chapter 13, 'Intersegmental co-ordination' were longer than the other chapters, and dragged a bit for me.
Overall, I recommend this book highly as part of the canon every aspiring phonetician should cover, though I wouldn't choose this as a first work to read in phonetics - Ladefoged goes down more easily, in my view. _Principles_ is, however, a very rich and definitely worthwhile reference to have in your personal linguistics library.