I think it might be interesting to run a roleplay in a corner of white wolf's Exalted setting known as Malfeas. For the uninitiated, Malfeas is a prison dimension for the losers of the war between gods and demons, made from the bodies of the great demon lords themselves, the Yozis.
That sounds a little complicated, doesn't it? Well really, hell is kind of simple. It's a big city, made of brass and constantly shifting around on shells of reinforced concrete and granite on an endless desert. The sky is black with obsidian roads, and the sun is green. There are no days or nights in hell, and the only permitted timekeeping mechanism is a particular breed of demon that wails in horror at the prediction of its own fate every sunrise and sunset in creation. But even without the passage of time, there is indeed a source of darkness in hell. The Ebon Dragon, shadow of all things, he who blocks out the light of the hell sun, and brings with him the call of darkness Erembour, who sings a song that tempts even demons to a greater and more corruptive darkness.
Lieger the hell sun scours the face of Malfeas, the demon city, with its radiance. Upon the endless desert Cecylene, countless first circle demons live out their days in debauchery, decadence, terror, and even glory. But never silence. For silence in hell brings the silent wind Adorjan, the quiet death which can devour entire layers of the demon city.
The game would mostly be a day in the life sort of game, chronicling the lives and times of various denizens of hell. Hell is basically a place that makes very little sense, but has a very deep mythic logic to all of it. It is a place defined by massive catastrophes, and perverse creatures. Players can play either demons, humans who blundered into hell or perhaps mortals who were spirited away.
Some basic principles:
Hell is not the afterlife: The dimension of Malfeas was created as a prison for the losers of the war between demons and gods. It is not meant for humans, and has very little to offer humans. That said, every new years, portals to hell open up all over the world, and foolish mortals can blunder in. And although a human cannot go to hell of simple and mundane wrongdoing, dabbling in the art of demon summoning can result in being taken to hell for the amusement of demons. (Although since mortals don't have very much value at all in hell, being on the whole much more fragile than demons, they tend to get quickly tormented to death, and not actively sought out. Except by demons with very specific tastes.)
Hell is made of demons: Malfeas imprisons 23 Yozis, posessing between them 360 souls. The 360 third circle demon princes themselves are composed of the combined existence of the 2520 second circle demons. Below the carefully ordered ranks of Yozis, Third Circle God Monsters, and Second Circle Demons, lie the numberless masses of the first circle demons, slave races and extensions of the imaginations of the greater demons. First circle demons provide the endless chattel to keep the ruling class of hell entertained, but they are far from stupid. In fact, many, if not most, first circle demons are smarter than the average human. First circle demons are frequently summoned by mortal sorcerers, and such beings relish those rare opportunities, for they give a demon, however brief, a chance to escape hell and cultivate influence in a realm where its powers are actually impressive.
Hell is very dangerous: Between the silent wind Adorjan, the acid sea Kimberry, the seductive songs of Erembour and the cataclysms of Isidoros that collapse entire layers of hell, a demon who does not know when these threats are coming lives in constant fear. If the Yozis and third circle demons don't kill a being caught in hell, surely the political machinations endemic to demons will get a good deal of killing and dying done for the sake of honoring Malfeas.
Demons can live forever until killed: The cruelest joke of their existence, for demons, is that they could be just as immortal and glorious as the gods, but instead they must live lives of constant terror and futility, before being ground between the toes of the Yozis. Ambition is in the very core of what a demon is, for there's really very little else a demon can aspire to. A demon who dies reincarnates in a lower, more pathetic form in the pits of hell, remembering well any former glories they attained, and raging to get what succor they can possibly take from their existence.
Hell is a prison: Demons cannot escape hell, save for one caveat: summoning. On inauspicious days, or simply for a sorcerer of sufficient power, portals from hell into creation open up, giving demons a brief, glorious taste of a better world, before they're swallowed back up into the hellish grind. Certainly, a demon often spends its entire term in creation in bondage to a sorcerer, but at least such a condition gives a demon a chance to accomplish something of note, rather than having to face the endless futility of hell. Demons tell many legends of those among their number who broke free of inept sorcerous binding, and were permitted to roam free for a brief, glorious moment in creation, before the servants of the gods hunted them down and sent them back to hell.