This book is most ostensibly not a work intended to provide a layman's knowledge of Bach. The book assumes a fair knowledge of Bach and his oeuvre, as well as a thorough knowledge of music theory and general instrumentation. Cristoph Wolff has written a thoroughly satisfying and extraordinarily comprehensive summary of Bach's professional and personal lives. I found that despite the book's intrinsically serious tone, reading it as a whole felt not like a biography, but a story that us Bach fanatics wish would never end.
This book is thoroughly impressive in both its scope and its detail, though the numerous tables cataloguing Bach's work from the various periods such as Weimar and Cothen are not as well integrated in text as one might hope. Where Wolff makes the occasional reference to the tables, I as the reader desired to see more comparison and analysis of various works in each period.
It is also immediately apparent upon even a glance through the index that Wolff dedicates much of his analysis of Bach's major works to Bach's vocal music, and notably less space to Bach's instrumental and keyboard/organ music. As we know, Bach's Fugue "the Great" in G minor, BWV 542, is a towering masterpiece of Bach's (and Baroque) organ music, but Wolff hardly affords it the analysis it demands. He also neglects to develop much depth of analysis with Bach's instrumental works. For example, we know that nearly all of Bach's solo and multiple piano concerti have their roots in previous concerti, but little attention is paid as to why Bach chose to transcribe to piano(harpsichord), why he selected the works he did, and whether there is a distinct method/pattern to Bach's transcriptions.
Wolff does do, however, an exquisite job of analysis of Bach's vocal music, exploring the depth of Bach's passion for writing cantatas, and how skillfully he was able to interpet his vision of the words into music. Wolff provides numerous glimpses of Bach's organ expertise, especially in the field of repair and construction. These descriptions do require some prior knowledge of how an organ produces sound and how it is played in order to be enjoyed to the fullest. The book also does a magnificient job of exploring and relating the various and primary influences on Bach's musical development and style. Wolff provides an insight into the influence of Dietrich Buxtehude especially, as well as that of Johann Pachelbel and the numerous older Bach relations. Much has been heaped upon Mozart's child prodigy fame, but even those of us for whom Bach is a perpetual favorite, know little about Bach's formative years, and Wolff gives a very comprehensive look at Bach's musical training.
Wolff's small digressions notwithstanding, this book is truly one every lover of Bach should keep in his library. (And reread every so often!)