Terry Pratchett is a safe buy. You'll get a few hours of escapism, and some funny moments with familiar characters. There'll be some hints of popular culture in the jokes, but generally little of relevance to the world outside the book (sure, there are some exceptions, like The Truth, but in general...). The latest Discworld novel to hit paperback is Thief Of Time, which, amongst others, riffs on James Bond, Star Wars and Hong Kong film. It's a typical Pratchett story where an apprentice is guided by a wiser figure to some form of redemption. We get to meet some old friends along the way, with cameos from characters who've starred in other novels, but here we've got four or five main characters, only one of whom has had a major role in a previous novel.
It's interesting that Pratchett is making me think of his books in terms of film, or a TV series. Like Buffy, we've followed the Discworld through growth, pain and change. We have a familiar cast of characters, both good and evil, that can be drawn on at will. Pull any from the rack, mix them up a bit, and bingo - instant story. To change the metaphor to food, this is Delia - not a Michelin Star. After finishing Thief Of Time it's hard not to think that the Discworld is getting a little tired, a little stale. The characters come onto the stage, do their little dances in the way we expect, and then wander off, almost unchanged, to sit on the rack until the puppet master calls on them again.
Mind you, I'll probably buy the next one anyway.