Greyhawk vs FR
The user JohnBiles at RPG.net had, I think, a good reply to this issue of “Greyhawk vs FR” which I will copy below (I hope he does not mind). I think Nightscreed’s essay on the topic of defining Greyhawk is also useful, though far more one-sided in a pro-Greyhawk and anti-FR way.
Greyhawk has a central story to its history and the Forgotten Realms does not.
Greyhawk’s history basically starts with the Suel and Baklunish empires locked in seemingly eternal war. They then blew each other to tiny bits and everything sinks into utter barbarism and the Suel scatter east across the Flanness, while the Baklunish squat in the ashes and claw their way back up to civilization slowly. Meanwhile, the barbarian Oerdians conquer the Flan (think ‘Celts colonize Pre-Colombian North America’ ) in the Flanness while the Suel refugees end up at the fringes.
Eventually, an Oerdian empire, the Great Kingdom of Aerdy arises and reunites most of the Flanness, while the Sheldomar valley is reunited by a state of mixed Suel and Oerdian origins, and a great religious state arises in the west in Baklunish lands.
All three states break apart into pieces under their own weight and now those pieces break into pieces and now the Flanness is full of quarreling states that are themselves in many cases in decline.
Mix in the rise of an evil god and his evil kingdom (Iuz), a wizard obsessed with maintaining the ‘balance of good and evil’ (Mordenkainen), a nutjob wizard who imprisoned nine demi-gods (now free and he’s become a god himself, Zagyg), the greatest of Dungeons (Castle Greyhawk) and you’ve got Greyhawk’s present.
Greyhawk is in a period of breakup and decline. Only nasty kingdoms are actually growing stronger (the Pomarj, the Scarlet Brotherhood, Iuz, etc) and many kingdoms are losing control of their outer fringes.
By contrast, I can’t think of an overriding story of Forgotten Realms’ history. Rather, every region has its own local history which doesn’t really fit into any larger pattern of rise and decline I can see beyond the existence of now-destroyed ancient empires which often involved races which have lost control of the world.
Who Rules the Roost
Humanity dominates Greyhawk, even if Humanity is currently divided against itself. The Demi-Humans are largely confined to the fringes. (Indeed, humanity is so much in charge that distinct races of humans exist and have significance) [Edit – For reference, the human sub-races are Suel = Blonde and Pale Skinned (Scandanavian), Baklunish = Dark haired and Golden Skined (Arabic or Turkish), Flan = Dark Wavy Haired and Bronze Skin (American Indian), Oeridian = Blonde to Dark haired, Olive Skin (Spanish)]
Humanity is the largest race in the Realms, but they don’t hold quite as dominant a position as they do in Greyhawk.
The Role of Neutrality
The Forgotten Realms is about Good vs. Evil; neutrals pretty much tend to either side with good or get bulldozed.
Greyhawk is mostly neutral people with really good or evil places a lot more rare. (Though evil kingdoms seem to be gaining ground of late.)
In Greyhawk, there is a lot of really potent magic, but ordinary life is rarely shaped by it. Most people are dirt-farming peasants who may well know a spell-casting local priest, but that’s about it for magic.
In the Forgotten Realms, there doesn’t seem to be quite as much huge magic as Greyhawk, but you’re more likely to run into it, especially in the 4E magically devastated Realms.
Pretty much, in Greyhawk, any secret group is probably either evil and wants to kill you or is neutral and trying to maintain the balance. I can’t think of anything even vaguely equivalent to the Harpers on the good side.
In Forgotten Realms, there are some good aligned groups which might help you out. In badly run FR campaigns they won’t leave you alone.
There is no overgod in Greyhawk; there is one in Forgotten Realms. Demigods seem a lot more common in Greyhawk to me than FR but I am not sure of that.
Read more: http://www.enworld.org/forum/showthread.php?540556-Mike-Mearls-on-Settings/page6#ixzz4feJnVMJJ