I'm a pretty big fan of this book. It does sortof amount to the grown-up equivalent of doodling "I <3 BACH" on one's Trapper Keeper for 300 pages, but Gaines makes a good argument for Bach's genius, and I've always been a big fan anyway. (Although no one will convince me that the <a href="http://www.youtube.com/watch?v=b0wd0EN2rBA">Ricercar is a total success, man. Six voices was too many even for Bach.)
The history is solid and the story is good, but what really elevates this for me is Gaines' descriptions of some of Bach's work. It's very difficult to write about music, which makes it surprising that so many people try to. Gaines really nails it; he makes you desperate to hear the pieces he's raving about (I spent several hours on the couch reading this book and listening to each piece as he got to it), and once you hear them, crucially, you think, "Yes: he's totally right about that, whatever, catabasis there." (Except in the case of his defense of the Ricercar. A for effort, bud.)
For what it's worth, the best writing about music I've ever seen is the treatment of the Trout Sonata in Vikram Seth's An Equal Music. I'm sure you were wondering. I don't remember anything about that book except that now I'm a huge fan of the Trout. (Incidentally, one of the many times I fell in love with my wife was while watching her play that piece.)
The essential question in Gaines' book is the difference between music as mathematics and music as free expression, and that's one that's fascinated me ever since Music Comp II when we learned all sorts of arcane rules for how to modulate between keys. It was extremely scientific; that might sound awful, but it's not...necessarily. In my hands it was pretty awful. Bach, on the other hand, was obsessively mindful of all this, but you don't notice it at all. Some think these rules - the dissonance in a tritone, the consonance in a fifth - are the secrets to the universe, no different than Einstein's E=MC2. That's bullshit, but it's really interesting bullshit, isn't it?
Added and weird bonus: this book also started one of my very rare and much-wished-for literary conversations on the T, from a New England Conservatory student of indeterminate gender. The bad news is that it reminded me: the sort of person who comes rushing over to talk about your history book with you is also the sort of person who insists on pronouncing "Bach" all pretentious-like. Just say it Bock, dude(tte?). You sound like the kind of douche who pretends to like the Ricercar.