I think that you can probably play a Discworld game fairly straight - Pratchett definitely cut back on the non stop punnes in the later books and tackled some serious subjects. A gritty Watch procedural game would be fun to play.

Well yeah, but the whole essence of Discworld is that underlying tongue-in-cheek parody and humour. I'm rather surprised it was a whole system in itself, rather than a sourcebook for an existing system