If I could steal credit for a book and claim it as my own, Reaper Man would most likely be it. This is the point, I think, where the Discworld novels stopped being entertaining light reading, and really became literature. It's a very subtle shift from the little parodies of science fiction and fantasy conventions of things like The Light Fantastic to the rich satire of a book like Jingo. Behind the story of Death being fired for having developed a personality, there's a clever little parable about what it means to be human, to be alive, and why the man locked in the tower watched the flight of birds.