This is really the first full Discworld book that I've read. I've read comic book adaptations of one or two, and a little bit of other Pratchett, but I haven't really done the main series before. I was pleasantly surprised. I had expected it to be funny, but I hadn't expected the writing to be quite so good, and I had figured on coming into the middle of the story.
In fact, while prior knowledge of Discworld is probably helpful in catching some nuances and details, it really isn't all that important. Most of the characters were clearly created specifically for this novel, and there isn't any apparently-critical continuity. If you accept that it's an oddly whimsical little fantasy world, that suffices for the purpose.
This book is an extended musing on Time, in all its facets. Much of it is simply whimsy, but the fantasy is underpinned with just enough science to feel curiously right. This isn't hard science fiction, mind -- Pratchett is much more interested in telling a good yarn than anything else -- but where it is convenient to make a bit of scientific or philosophical sense he does so. The result is much more satisfying than a typically random confection of fantasy.
The story is complex and winding, and takes its time. Despite a rather apocalyptic plot, it never really rushes -- after all, the subjective nature of Time is laced throughout. But the writing is consistently delicious, and worth savoring.
(Why all the flavor metaphors? Suffice it to say, the fourth principal element of the universe -- chocolate -- features prominently in the plot.)
Of course, Pratchett is known for his humor, and the story does not disappoint in that regard. The writing ranges from droll to laugh-out-loud funny. Even as the situation gets grimmer, it gets funnier -- about halfway through is a scene that I can only describe as the perfect melding of Monty Python and the Coneheads. Every character is well-drawn, and everyone gets a good arc.
No, it's not a book for the ages. But it's well worth reading -- a lot of fun and chewier than brain candy.
As for the recording, it's an unabridged reading on eight longish cassettes. The reading style is a tad odd. There are five principal readers, and each one is mainly focused on a particular character's plots. But it isn't consistent, and it isn't the usual "cast" style of recording. Each chapter is read by a particular reader, so you often have to deal with a character being read by someone other than their usual voice. That's sometimes a bit distracting. But the readers are good, and each is well-cast for their principal role, so it generally works.
(And actually, there is a sixth reader: Harlan Ellison plays The Voice of the Snarky Parenthetical Comments. This, too, is excellently cast.)