This was inspired by Crucible of the Gods, but I think it’d make a pretty sweet campaign setting...
It is the End Times. The world of Surridan is overwhelmed by floods, plagues, meteoric storms, and famines. The gods have deemed their creations unfit and seek to start anew, a cause which unites good and evil deities in a merciless wiping of the slate. As the sun flickers out, the sea turns to blood, and the vegetation grows blackened and scarce, desperate races and once-proud cultures seek strange alliances and dangerous pacts to survive. Angelic killing squads scour the surface of Surridan exterminating at will, while devils overrun the Underdark to drag the corrupt into Hell’s maw. Only a handful of prophets scattered across the realm have managed a tentative truce, requiring not the offering of blood or prayer, but proof. The few gods who will listen must be convinced their children still deserve to exist. The adventurers, treasure hunters, gladiators, and mercenaries of the old world have risen to meet their demand, recognized now as an exalted class of Redeemers, scaling ever-more-impossible climbs, besting increasingly horrendous foes (including the new races of the gods, designed to replace them), delving into deeper and deeper dungeons, and returning with grander and more prodigious offerings for the fanes and crucibles to show the creators they are worthy. Some are given cause to rejoice, becoming fanatical in their faith, while others lose all love for their makers. Madmen turn to undeath and golemizing as means of salvation, while others secretly pursue the only real solution: godhood.
Notes: Firstly, I like justifying adventuring, dungeon crawling, and D&Disms as vital to the world's survival. I think the moral shift which has fairly ruthless and greedy dungeoneers becoming these redeeming heroes really takes the moral and spiritual side of the game (RP) into some really grey, great territory- and must repurpose a lot of once holy and learned orders, much to their chagrin or dislike perhaps. How the population has reacted to the end times, how these great leaders, now Prophets, are on their knees begging must have all sorts of tolls on the races. I like how good-aligned angels and evil-aligned devils are on the same side, agents of Armageddon, is an even more fun way to use all of the Monster Manual than calling angels neutral soldiers. These angels also have faces and legs (see MtG). The idea that part of their trials, which have been given no timetable, include fending off new races the gods have made to replace them is amazingly ripe. And, as always, there's people who want to be liches and sentient golems (new history for warforged, perhaps, not as soldiers but as men and women attempting to endure beyond the apocalypse... maybe more selfless ones imbuing their consciousness into machines in order to better face the trials- calling into question the value of mortal races and machine).
This one is just something I've been playing with...
Garuul is a prison crafted by the majority of Good and Unaligned pantheons. For his sins, Man has been interred for all eternity in a brutal world of iron expanses and steely outcroppings, whose red skies are caged in barbed crosshatch and all means of planar travel have been barred. They are not alone... Here Avandra, once goddess of freedom, is locked in the impenetrable core of the planet. Melora thrashes chained at the bottom of an acid sea. Mad Erathis, civilization incarnate, survives as dismembered heaps entombed in the four corners of the uncivilized jail-land. Ioun, perhaps the only genius capable of working out a means of escape, has been lobotomized, a titanic, blithering idiot slowly shuffling across Garuul’s surface- impervious to harm, an unwitting natural disaster than tramples and crushes as it mumbles. Proud Kord witnesses it all and weeps, the strong one now crippled and paralyzed on the highest mountain top. The fate of the gods mirrors their children’s grisly and troubled hardships, made all the more difficult for their cellmates: other races with unforgivable histories who’ve been thrust onto Garuul numbering the orcs, tieflings, dragonborn, and races more savage and alien still (space for a new interpretation of the Thri-Kreen as more cockroach-like and Shardminds as failed alien invaders). Despite the absolute oppression, some prisoners still seek freedom, delving to reach or repair their broken gods, to invent new magic and technology to take them from Garuul, supported by the black-market run by the slippery, mercantile drow hopping in and out of Garuul by the graces of one of the last surviving champions of evil: Lolth. Even she is hard-pressed, as are the would-be escapees, for Garuul is guarded over by two watchtower worlds, the Feyward and the Shadowcell, whole planes worth of guards and wardens.
Notes: I think Garuul utilizes a lot of 4e assumptions in new and interesting ways. First off, it puts a lot of the PHB1 races in the forefront and welcomes some of the weirder and more monstrous as baseline. It also more or less excludes elves, dwarves, gnomes, and the children of the gods who've now turned on Man and his creators. That's not to say a particularly sympathetic or bad member of the race couldn't be cast into this hellhole, but it's not common. 4e gods are front and center, and again D&D's need to delve, crawl, adventure are set into the core assumption- you must find and heal your gods in order to escape, or help the organizations working on new magic and technology to escape, or maybe the opposite, become kings of the damned. The drow escaping race-wide imprisonment to be the suppliers in this prison-setting also leaves a big spot open for them (and they do seem to be getting a lot of 4e coverage). And retooling the mirror worlds of Feywild and Shadowfell as watchtower planes, basically the prison walls and yards beyond Garuul itself, leaves a lot of fun reimagining of fey and classes like wardens as actual wardens, the whole Primal power source made out to be oppressive. Same with the Shadowfell, and the Shadow power source, undead, vampires, vryloka, shades, all of them kind of like the other have of the penal system, maybe fashioned more like laywers and judges on cosmic scale. Or maybe we can reserve that for Hell, devils like lawyers and judges, torturing Garuul with mocking trials. Just kind of riffing now, but it can be taken a lot of places.