My 4e playtest from levels 1-30 worked like this:
There are 1-3 encounters, and then the character's level. Ideally, this means 1 level every session or two.
The story is thus: the PCs were all dragons in the service of the Dragon Goddess of Light (think Bahamut, but with bewbs). A war erupted with the Dragon God of Darkness (think Tiamat but with Glenn Danzig's pecks...oh wait...)
The Dragon God of Darkness won. So the Goddess was tossed into the underworld, and the PCs (executed by the Darkness god) soon followed.
Now, the actual campaign started with the PCs being the characters they made, waking up in a field with no memory. They are humans/elves/dragonborn/whatever who know they were friends once, but know nothing else. They travel through very desolate lands (ala Shadow of the Colossus) accompanied by the ghost of a little girl (actually the Dragon Goddess, also w/ amnesia), fighting through "boss monsters" (also similar to Colossus).
Eventually, they notice the ghost of the little girl "growing up" (i.e. sounding more mature) after each battle, and they soon realize they are in the Underworld. Each boss they face gets them closer and closer to the gatekeepr of the Underworld: who just so happens to be the Dragon God of Darkness.
A lot of the symbolism and monsters had a very Egyptian afterlife bent. Ruins of pyramids, weighing of the feather to pass on to the final boss, etc.