This book is a strange combination of some interesting content (especially the part about the works; the biographical information is dry and gives no idea what kind of a person Bach was), and some very misguided choices in translation. Aside from the occasional translation error, the translator seems not to realize that the "historical present", which is used in German, does not exist in English (other than rarely). This gives, as another reviewer pointed out a sensation of cognitive dissonance. As I translator myself, I'm used to seeing this is French (the language I work from), but when I read a French book using this, it is rarely as disturbing as it is here. The translator should have normalized this into English, that is, using the past, but also should have normalized the disturbing shifts of time from the past to the present that occur on nearly every page.
The biographical section is, as I mentioned, dry and static; you get no feeling that Bach ever ate a meal or went to the bathroom. It is fact after fact, date after date, written document after written document. The parts about the music itself are more interesting, but the overall feeling this book leaves is one of confusion. The decision to separate Bach's life and work is curious; the two were intertwined (especially because the author talks so little about Bach as a person, there's nothing else to hold up to the light).
All in all, this is not a good book for someone wanting to understand Bach's life. Alas, in spite of the many books about Bach, not many of them do so. Others are also plagued by translation errors, or academic prose, and a real humanist biography of Bach is needed.