I usually don't really like books about music and musicians. The simple reason is that nine times out of ten, those books fail at describing music, conveying what it's like. It's hard to do. I mean, try to explain to someone who have never heard Jimi Hendrix what he sounds like. You have to give to GRRM, though, he did a brilliant job with Nazgûl in Armageddon Rag. You can almost hear their stuff in your head, even though you realize they are a fictional band. If you've only read his ASOIF novels, pick this one up -- it truly shows how a versatile and brilliant writer he is.