Terry Pratchett is a genius. That is; he used to be one. The first five-or-so books of the Discworld series were nothing short of close-to-genius, laughing-muscle-training witful writing.
Too bad, things have changed...
Douglas Adams (the author who indirectly introduced me to Terry Pratchett) has written the ultimate work of humour: The Hitchhikers guide to the galaxy. But also here, only the first two books were really worth reading. The funny rambling goes over to being "I have seen this before" material - it's still funny, just not as new, and to a lesser degree unpredictable.
I just hope that authors realize that even though they CAN make money of a group of loyal fans, maybe they SHOULDN*T.