I am a big fan of Robert Christgau's books, especially his three Consumer Guide compilations of the 70s, 80s, and 90s. In these books, there are capsule reviews and grades of literally thousands of records--mostly rock and pop, some jazz (fusion) and country (crossover), no classical. I have found all three to be invaluable resources for finding new music and have purchased dozens, perhaps hundreds, of records over the years based on Christgau's recommendations with very few disappointments. Moreover, the reviews are so witty, incisive, and well-written that I simply enjoy them for their own sake. I second the Greil Marcus as well.
I'm looking forward to plunging into that Neil Young opus.