For most of my role-playing life I have written my own material, so by now the D&D setting is extremely detailed... it is only recently that I have even looked at the wealth of material other people have written, and I'm finding it fascinating to now explore the Forgotten Realms, Greyhawk and all the rest...
I now run a weird combination game, starting off in a 2nd partially-homebrew world, which draws on a lot of published material that's set in a 'generic' world rather than a specific setting; and from which you can travel to other worlds - both my original one and published settings - via a kind of magical portal system.
If anyone wants to sample it, do let me know. Someone else is DMing at my weekly session (and our campaigns tend to run for a year or so, he's 4 weeks into it), so I'd quite like to run something 'play by post/e-mail' - any takers?