This year's Rock and Roll Hall of Fame class included R.E.M., Patti Smith, Van Halen, The Ronnettes, and Grandmaster Flash and the Furious Five. The problem with this list? To some critics, it looks like a game of "One of these things is not like the others" a'la Sesame Street ... or maybe that just one of these things belongs here. While few dispute R.E.M.'s place in the Hall, the remaining classmates have proven more controversial — does rap music belong in the hall? How much commercial success do you need to get the nod? And just what is rock music, anyway?