I picked up the most recent Eberron supplement call City of Stormreach. It is a frontier city on the tip of exotic Xen’Drik (where the Shadow Company is originally from – the shattered land of the Giants). Stormreach is presented as a microcosm of the main continent that most of the published material is centered on. Ex-pats from each of the main countries tend to live in their own small enclaves—and the hatreds of the last war still simmer. The Dragonmarked houses are represented, but not dominate. The port was a pirate’s haven built on ruins. It is still is under their leadership, just in a more respectable manner these days.
You folks have gotten a taste of Sharn – a huge city rising thousands of feet up in the air. It is the Ptolus/Waterdeep/Greyhawk/Ramal/Tabolport of Eberron campaign world. A big city to use as a backdrop to the campaign world.
It lead me to an interesting observation – with these two cities a GM could run almost the exact same campaign with one big difference – each offered a completely different level of what I will call “PC-centrists” of the campaign. With Sharn, you use the Lightning Rail, flying ships, and other magical convinces to make the world smaller. The published adventures really emphasis this approach to whisk the PCs off to all parts of the world. However, Sharn is huge – you will likely not be “the only hero in town.” You can make political intrigue as you like, but it will probably only involve one or two groups since it is a city of a million souls.
In Stormreach (I think the population is about 30K), you have it boiled down to a smaller area (with an exotic continent just outside your doorway). By crossing a couple of streets you can experience different aspects of main nations in the world. More intrigue naturally results as the PCs will be a force in the area. Do they stay unaligned (for hire)? Do they throw in to a Dragonmarked House? One of the enclaves with strong nationalistic pride? If they dig out some relic from under the city or out in the jungle, how will all the groups react.
I throw this out there since I with Eberron and the Columbus group have used the SuperCity as a base in many campaigns. This is an interesting alternative approach the allows you to use all the material of your more “civilized” part of the game world in one small place—a frontier city in a foreign, untamed land.