The New Republic Online: Rolling Stone Unplugged presents an interesting take on long reviews vs. short reviews:
With the proliferation of file-sharing technologies, young fans have a "celestial jukebox" that gives them instant access to virtually any music at any time. In this brave new world, less is more. Readers don't need 7,000 words on a band to decide whether to buy its new album; they need 70 words to decide whether they want to download it.
I'm torn- it's true that I've discovered a lot of great bands by downloading songs (Interpol, Rye Coalition and Spoon are the most recent), but I like reading long critical pieces that I can remember when I'm flipping through CDs at a store. A 2 paragraph review isn't as likely to stay with me as a 2 page one.