Oh, and before I forget -- one recurring source of humor in Pratchett is a sort of comic-fantasy angle on steampunk, in which some blend of alchemy and magic is used to recreate technological items you'd not expect in a fantasy setting. This sort of thing is sprinkled throughout all the books -- you see it from the very beginning, with foreign tourist Twoflower's "camera" (a box with a tiny magic imp sitting at an easel, painting very fast) -- but it tends to be particularly thick in the Industrial Revolution (http://www.lspace.org/books/reading-order-guides/the-discworld-reading-order-guide-1-5.jpg) books.