So I thought I'd write a separate thread about the essence of Greyhawk, and what it means to me. A thread where people can discuss the essence of Greyhawk (whatever that might be) instead of complain about Dragonborn.
I would start by saying that Forgotten Realms is a great default setting for 5e. It has a long history and abundant products and novels that can be used to fill it out. We have people, many of them active on this board, who love all of this history, lore, and canon of the FR and can recite it chapter and verse; in addition, FR has an excellent wiki. I often make fun of FR for its various spellplaguesunderings and what not, but for what it is (the uber-setting, the generic D&D setting) it is great. So my a priori assumption is that Greyhawk shouldn't be that. We do not need TWO generic settings. So, with that caveat in mind, what is Greyhawk to me?
1. It's humano-centric. This doesn't mean that all PCs are humans, just that humans are the overwhelming default, and that great care has to be taken when deciding on non-standard options given the likely choices for adventuring.
2. It's small in scale. You aren't saving the Realms; you're making a buck. I say that partially in jest, but this is partly the aspect of Swords and Sorcery that needs to be played up in a Greyhawk setting. Small scale DOESN'T mean small stakes, however. You can save (or destroy) the village; but there should be a lot less of the "saving the world."
3. There's always something bigger, badder, and more mysterious. This is related to (2). You will never have the power of the Mages who destroyed the Sueloise civilization. There will always be the past glories or dangers, the stories of Vecna and of giant ships crashing from the sky, of beings that strode across the landscape, that are told around the fires at night.
4. Civilization is tenuous, at best. The great powers and empires are in decline and their best days are in the past, and it is always questionable if the forces of civilization will hold off the entropy and darkness. Progress is not assured. The forces of destruction are constantly howling and looking for a way in, and, more often than not, they are about to succeed.
5. People just don't like each other. What do I mean, "people?" Well, everyone. There are long-standing divisions; Suel, Baklun, Oerd, Flan- and that's just the humans. Different elves can be distrustful based on geography or type (what is a Valley Elf doing outside of the Valley?), and demi-humans and humanoids will be met with more (or less) suspicion depending on the location. But see ...
6. People should be suspicious. So civilization is tenuous, but also spread out. The Flanaess is huge, and poorly controlled. That means that outside of a few of the larger and cosmopolitan cities (such as Greyhawk) people will tend to be suspicious of outsiders; after all, if survival is perilous, you, too, would be careful about extending hospitality to people you don't know.
7. Greyhawk is a a DIY sandbox. This is kind of the key to what I think is a good Greyhawk; it should provide adventure hooks, but not prescribe what adventures there are. It should be the canvas on which to paint your own campaign.
So, what does Greyhawk look like? Like the first Conan movie- vast areas of emptiness, mysteries that abound, small in scale. It's not Tolkien, it's Lieber or Howard. But most importantly, it is the space to create your own Greyhawk.