Alex Ross hits another one out of the park (at least that's my opinion about 1/3 of the way through, and I don't see things falling off) with his new book Listen To This. What's really fantastic about the book, aside from all of the great specifics, is the general philosophical approach to musical art that Ross takes in his commentary, explanation, discovery, etc.--he simply loves music, all of it, and makes no a priori distinctions about what can or can't be good.
Excellent overview from the New Yorker here.
There is even a FREE online audio guide on his website.
Read this, soon.