I was thinking more about Monstrous Regiment and how it's very much a satire of war, gender, and religion and even the fantasy genre itself. The purpose of satire is generally to make fun of something in order to bring people's attention to it and correct it, and Monstrous Regiment, while it's not overtly preachy--as it shouldn't be--it does raise questions though most readers are likely casual enough that they'll only read it for the laughs at the superficial jokes.

Obviously, Monstrous Regiment lambasts stupid wars and the nationalism that tends to drive them--the Borogravians attack everyone just because they see the world in terms of Us and Them. It also raises the issue of gender, as by the end of the book pretty much every capable character has turned out to be a woman in disguise. The only main character who isn't a woman is Blouse, and I have issues with his capability, so it's a moot point. ;)

And of course, there's Nuggan and his Nugganite law, a stupid religion hung up on the law and the proclamations of abomination handed down from above. Jigsaw puzzles, the color blue--the list of abominations unto Nuggan gets progressively more ridiculous until the people are forced to break them just to go on living their lives, and made to feel guilty for doing so.

And it also pokes a good deal of fun at the cliche fantasy ideas--as somebody else mentioned, they weren't sure about reading it because the back cover threatened just another girl dressing as a boy to do the forbidden, but Pratchett takes that idea and turns it on its head, making it new and interesting again in Monstrous Regiment.