I think an RPG setting should have a default campaign concept. For D&D, this would be "a party of adventurers goes down into underground ruins and caverns full of monsters, kills those monsters, and takes their stuff." For Shadowrun, it would be "a party of Shadowrunners gets hired by Mr. Johnson, hacks their way (in more ways than one) into a corp facility, performs some objective, and bugs out, and most likely at some point gets double-crossed by their employer." This sort of thing provides an immediate hook for both the players and the GM. The players know what sort of characters they're going to need to create, and the GM knows what sort of adventures to write. Of course, a good setting will support more than just this one type of story. Still, it provides a good place to start, and a place to return if no other options show themselves.
For the World of Ruin setting, the default campaign concept is a group of Zonerunners--adventurers, most likely based in or around SanTiMA, who venture into the Dead Zone to retrieve items, creatures, or other resources, or simply to learn more about its mysteries. In between such trips, they engage in ancillary quests within SanTiMA's society, and perhaps from time to time they come into conflict with the forces of Angel City. There is room for action and adventure, but also mystery, intrigue and wonder in the Zonerunner campaign.
The Dead Zone itself is a region located between Angel City and SanTiMA. It occupies the area of south Orange County and north San Diego county, and probably extends inland to some degree (I haven't actually mapped its boundaries yet, and really the very idea of firm boundaries goes against the nature of the Dead Zone). It serves, among other things, as a buffer between those two city-states, and has so far prevented all-out war between them.
Despite the name, the Dead Zone is far from dead, though it is quite easy to die there, particularly if one is unprepared. The fabric of space-time is weaker there than elsewhere, and it is common for banestorms to occur. These are usually very small, localized ones that only bring in a monster or two, or a small region of bizarre terrain, but some are larger and can swallow whole parties of adventurers and take them to other worlds should the GM decide to take the campaign on that sort of a radically altered course. Sometimes the unstable nature of the Dead Zone even interferes with the more subtle laws of physics, meaning that technology is prone to malfunction. Zonerunners are wise not to become too dependent on their equipment. Of course, going into the Zone without high-tech equipment is also not advised...
Magic too is unpredictable in the Zone. The mana level can fluctuate wildly from place to place, or even in the same area over time. Zones of Wild or Twisted mana are also disturbingly common. All of this chaotic magic makes the Zone a haven for mutated and tainted creatures, and even outright otherworldly monstrosities. Some of these are common and consistant enough to merit classification and scientific names, while others are unique individuals the likes of which are never encountered again. The GM is more or less free to invent whatever monsters he likes and put them whereever he wishes to.
All of this explains why the Zone is dangerous, and why people don't go there unless they're prepared for trouble. But, you might be asking, if the place is this nasty, why go there at all? The answer is that the same unstable spacetime, physics, and magic that make it so full of danger also make it full of resources. Some of the creatures that live there have powerful mana organs that can be harvested and used for alchemy. Similarly, crystals with strange properties can be found in the ground in the Zone (or even growing on the surfaces of ruined structures). The same banestorms that bring in monsters from other worlds also bring in items from other worlds. Some of these are magical, others utilize superscience far in advance of that of Angel City or SanTiMA. All of these are in high demand by researchers, and sometimes can yield insights directly to a suitably trained PC. The Dead Zone is, in effect, a giant outdoor (and sometimes indoor or underground) dungeon, full of monsters, traps, hazards, and plenty of loot.
The Dead Zone is also full of mystery. Its origins remain unknown, though Zonerunners occasionally encounter artifacts from before the Manaclysm (a word which I'm borrowing from GURPS Magic Items 3 because I like it so much) that may shed some light on how and why that great disaster happened. The Zone seems to be directly related to the Manaclysm, and there may be other Zones elsewhere in the world (expeditions sent outward by Angel City and SanTiMA rarely return with any conclusive information on this subject, if they even return at all).
So, in summary, the Dead Zone and the exploration thereof provides a focus for adventures, dangers to be overcome, material rewards to acquire, and plenty of opportunity for plot hooks into the larger-scale situation in the World of Ruin. I think that these three regions (Angel City, SanTiMA, and the Dead Zone) provide a good microcosm for starting campaigns in, with plenty of room to grow from there.
