That is, he doesn't make fart jokes and obvious one-liners. His characters tend to make witty or sarcastic asides, self-aware puns, and a lot of humor is very... I don't even have the words to explain it.

The reason I'm saying that is that Small Gods is "cerebral" in the sense that it's about religion, specifically where it comes from and where it goes. It has amusing observations on being an atheist in a world where gods throw lightning bolts through windows with notes attached saying "We Exist," and so on.

The other reason I'm trying to explain this is because I tried to get my sister into Pratchett, gave her Small Gods, and thought that I was amazed by the philosophy, when in fact the philosophy is just there for the jokes. So I guess I'm saying read it and enjoy it, but I don't think you'll suddenly change your worldview or anything.