>> ... but is instead a real person under all the funny prose. <<

I find this to be true of much of Pratchett, especially as he matures as a writer. It's very endearing (to me, anyway) - yes, weird and geeky people are indeed weird and geeky, but they are very human. And in a Pratchett story, especially the later ones, the oddballs are the ones who have what it takes to save the day.