Greyhawk of the early modules and gazetteer and boxed set era is undeniably awesome. It's really the myths of a larger world we never quite see that sold it for me. There were secrets known only to those who actually played in it down in Lake Geneva. Of course the published work was largely different, but so much of the design feel of the setting is at once the place of epic narratives with a big dose of historical allusions mixed with countless instances of humor in puns, inside jokes, and personal feel. The feel could put one off, but it is one of very few D&D settings which actually feel like they were built through play of a fantasy wargame and not just brainstorming without playing. There's no tie to an underlying theme in Greyhawk, no addressing of particular moral quandaries, nothing which our contemporary culture holds to make "good art", and yet it feels aged. Lived in. A real place. One with a history capable of being discovered because not only does what you do now matter, but also what everyone else has done before. The world was shaped, not dreamt.
I have high hopes Wizards will bring Greyhawk back, but it's original designer has passed on. There is no original voice for the setting now, much like Howard's endless imitators for Conan can never match his voice. It is not Conan without him and I fear it will not be Greyhawk without Gygax. But so much material exists even that hurdle may be overcome. The hard part is post-Gygax Greyhawk which has its own feel, its own highs and lows as well. Add in the LGG of 3e tying all original and 90s material together and Greyhawk now as a living work becomes harder to recognize as the earlier one. I don't know what we'll see of the setting next, but I'm actually rooting for small, game supporting, and focused. Something perhaps even very, very general on the big scale, and then with small pieces in regions setting down greater detail, yet still requiring DMs to fill in the proverbial map and make it their own.
I like the latest Wandering Monsters article for bringing up Silver Marches, possibly the best 3.x Forgotten Realms book published as a usable campaign setting. (of course that map is hideously outsized, but then I see Greyhawk as the original source of that trouble. I could see the 1:30 mile gaping hexes in Greyhawk cut down to 1:10, 1:12, or 1:15. Furyondy may as well be, I don't know, half of Europe otherwise.