Rock and roll will never die. Seems like a good subject for a Death sub-series book. Plenty of opportunities for pop culture jokes that Pratchett excelled at. It's also a fine introduction to my favorite Goth Disney Princess, Susan, Death's Granddaughter.
I was always a little wary of these Discworld books that blend our modern world into the timeless fantasy of the Disc though I'm not sure why. Men at Arms, Moving Pictures, The Truth etc. are all fine books. I view this one as akin to Moving Pictures because of the pop culture and the effect the phenomenon has on the citizens of the Disc, causing them to embrace showbiz/music biz with all their manic hearts. Of the two, I prefer this one, as there is more opportunity to get attached to the characters if you've been reading the full series. Susan is Mort's daughter and, if you read Mort, you get to see her make the same mistakes her father did.
The novel's themes are woven into both the story of the music taking over the Disc, as well as the personal family story of Death and Susan. Rock music as described here is something that acts on the non-logical bits of the brain, it moves you, makes you want to move, makes you feel young and rebellious etc. Susan is a character who loves logic above sentiment but is torn when she sees Death had an opportunity to save her parents from the accident which killed them.
There is also the element of rebellion in their part of the story. Death frequently shows his attachment to humans, adopting Ysabell, wanting to get to know baby Susan, etc., which goes against his role as the unstoppable force of death. Susan can't understand why she should not try to make the world better if she can once she has Death's powers.
This holds a place in my heart for my love of rock music but also because it is the book that got my teenage daughter interested in Discworld, giving us a shared pleasure in the books.