While SM may be one of the most enjoyable and "fun to read" DW books, I don't rank it up there among the top DW books, for some of the same reasons SWreader and others have stated.
To echo what Pooh and others have stated, 'true' enjoyment of SM, like Moving Pictures, Eric, Maskerade, and, to a lesser degree, Unseen Academicals, really depends on one's ability to 'pick up' the cultural references. I got most of the American and mainstream Brit references, but anything involving Welsh was beyond me. (Lspace WAS a great friend for this book). A twenty year old brought up on rap or Britney might find it entertaining, but not see what all the fuss is about.
It would probably make a great introduction to the series for the new initiate, especially one who knows something about R&R music of the 50s-70s, but it really doesn't demonstrate the full potential of the series that Pterry had already begun to achieve in some of its predecessors ("Small Gods" and "Lords and Ladies" in particular). Just compare this to the next Death book, "Hogfather," and you can see how far PTerry had advanced as a storyteller.
If one were to compare Pterry to Shakespeare (hey, why not?), one might think that "Soul Music" is his "Love's Labour Lost" or another "early-mid-period" comedy. If this was the only Shakespeare play you read, you might think it was a very good, very funny, well-written work. But then if you went on to read the later comedies like "As You Like it," "Twelfth Night," "Merchant of Venice," or "Much Ado About Nothing," or the great tragedies, you'd realize that LLV while great for its time (especially in comparison to other plays of the period) represents an artist still in the relatively early stages of his literary mastery.
J-I-B