Just adding to [MENTION=6787503]Hriston[/MENTION]'s post - I prefer to think of it as "the default 4e setting" rather than "Nentir Vale", because the Vale is entirely optional (it's found in the DMG and in the MV2) whereas the default setting permeates the whole game: the races, the classes, the monster descriptions, the gods, the sourcebooks (MotP, PA/B, Underdark, Open Grave etc).
Hriston is correct that the creation myth is loose, in the sense that the timing of events is obscure, the details of who fought whom where are often not clear, but the whole thing is very evocative and "mythic" by D&D standards (when The Plane Above came out I started a
thread about the "Glorantha-fication" of D&D).
The world was created by the Primordials out of chaos (analogously to the Greek Titans), and then the gods imposed form and sentience upon it. The Primordials turned against the gods who had imposed this permanence upon their creation (and therefore, by implication, were constraining he Primordials' freedom of action) and so the Dawn War ensued. The gods one, but were weakened: the cosmos contains many bound Primordials trying to escape and reassert their power; the gods and the mortals they created are imperfect and so mortal history is filled with the rise and fall of empires; and their are rumours of a coming Dusk War.
From the point of view of RPGing, a distinctive thing about the 4e creation myth is that the game is designed with the expectation that the PCs will, at least at epic tier, themselves engage with the creation myth eg by opposing gods or primordials, realising their epic destinies, etc. This isn't the case for most D&D settings.
