James at Grognardia has written an interesting post on the professor's legacy here. I would add is that given enough time, enough campaigns, a setting will wind up looking like Middle Earth in terms of organization and detail.
While Middle Earth was never roleplayed by Tolkien, he built Middle Earth piece by piece starting with a few notes on a language and a tale before World War I. The process is detailed in the History of Middle Earth series complied by his son Christopher.
Blackmoor and Greyhawk (the original version) were likewise built up the same way. Starting with a castle and a dungeon the world grew around them piece by piece.
It seems that the best settings are those that grow in this fashion rather than spring full flower from an author's mind. I am still trying to figure out the best way to help people jump start this process without having to go through 30 years of campaigning.