A setting, a campaign, even a single pick-up game is only as good as the DM.
There is no formula, no diagram, no mythos, not a damn thing that can make a setting good on its own. A good DM can make a bad setting good, can take a piece of crap published module and make it fun. It is a god-damn art. It isn't the setting that can get you into the game, that can keep a campaign going for weeks, months or even years, that can stir your imagination and make you feel the gold coins slipping through your fingers or startle the crap out of you when your character turns a corner, or makes you shout when you chop down that last beastie just before it takes your character down. A good DM does that.
My point is that there is no setting fluff that makes a campaign golden.
I detest Planescape, others love it. Greyhawk is my favorite published setting others have no time for it.
Setting fluff is subjective. You can have rivers that flow uphill, you can run into WWII German infantry attacking dinosaurs controlled from outerspace with a tree full of keebler elves on the side and it can be a fantastic game.
Or it can be a horrible game if the DM sucks. The DM is the setting. He breaths life into the words of a published world, he makes paper lions roar and unsheath their claws, he takes his imagination and becomes everything, the split in the player's backpack that rips while he is being chased by those paper lions, the rotting boards of the bridge the player runs across, swaying back and forth over a black and bottomless pit, the fraying rope, the feathered lizard creatures with spears that rush the player from the other side as the lions wait for their dinner to return. The DM is the town where the player rested, the kingdom the town resided in, the tribe of Ogres or clan of Giants, the number of coins stuck to the chest of the sleeping dragon.
There are no elements, no fluff, no story-line, that universally make a flavoursome campaign setting. The flavor comes from the chef, the DM and nowhere else. He can take your favorite steak and burn it beyond recognition or make it the so good your mouth waters at the thought of it.
All that you can do here is make a list of recipes that other people have enjoyed. A good chef, a good DM will know what to do with them. Use them, change them, maybe ignore them, but all you really need is that good chef.