Hmm, I agree - best of his recent books was "Night Watch" and that was... different, somehow. It had a lot more depth and meaning to it, instead of just poking fun at a new target. I think he needs to grow as a writer a bit more. But of course I read every new Discworld as it comes out.
Woo-hoo! Just checked Amazon; Pratchett's next book, "Thud!" comes out in October and it's a Watch book, which are always my favorites.