Do we know anything at all?

What makes great music? Is it a good guitar-line, is it the off-beat drums or the shivering vocals? Does it have to be new and fresh, original? One of a kind? What about the lyrics? Do they have to be understandable, yet deep? Can they be ambigous? Can they have no meaning what so ever, or be straight forward about the most simplistic things? Why do we appreciate certain types of music? Why do we select one particular band or artist? What about similiar music? Why won't we listen to that, but stay with our favorite band?