I write for living (albeit in Czech) and I don't think that PGs writing is bad. It is not artistically brilliant (unlike Douglas Adams'), but he gets his points clearly across, and uses a language that even foreigners with limited command of English can parse.
That's good in my opinion - in the same sense that hammer which drives down nails flawlessly is good. PG is not trying to write colorful fiction, he wants to communicate something, and he succeeds in doing so. It is still a hammer, not a statue of David, but there are good and bad hammers, and this is a good hammer. You wouldn't want to drive nails into boards with a statue of David anyway.
