I will say that in some cases there isn’t always a really strong story, sometimes its just his characters moving through one of those twisted themes. I like them all, you may want to start with the Most Von Lipwig story line (“Going Postal” and then “making money”) as at least the first one has a really great story line.
I love to pepper my reading queue with these books to keep all those books that take themselves seriously fresh and interesting.
I recommend reading them ALL.
OR listening to them. The two main narrators of Terry Pratchett’s books are Stephen Briggs & Nigel Planer and they take Terry Pratchett’s phenomenal writing to a whole new level.