Ranked in these QuestionsQuestion Ranking
Pro Funny like hell
Terry Pratchett has a way of putting every day situations into new contexts that makes you laugh.
Pro A complete universe
The books are (while not exactly based on each other) adding each a new facet to the imagined world of the Discworld.
Pro Consistent and well thought-out
Diskworld runs by its own rules, which sir Pratchett managed to describe and abide by. The whole thing is extremely hilarious and absurd while at the same time managing to be completely logical.
Pro Highly intertextual
There is an incredible amount of references to books/films/music/pop culture/historical events and figures/whatever else you can think of. Some of them are quite obvious, some you might get only a few years after reading the book - when you learn some small random tidbit of history or watch a particular scene in the movie. It's not only extremely enjoyable but also makes you feel proud when you suddenly connect the dots and figure out some obscure reference.