Having read the Eberron player's guide cover-to-cover, I'm ready to commit. I am now familiar with Eberron, Forgotten Realms (in 3rd ed.) and tangentially the Points of Light world, and have some old home-brew worlds kicking around. I know enough about Dark Sun to realize that my ideas don't fit very well with it - although I may craft a DS specific game some day.
Eberron has what I'm looking for. I have latched on to a few core ideas that I want to work with in a campaign, and Eberron has good representation of each of them. Being D&D, it what I used to call "too busy" - there is too much of everything: races, classes, monsters, threats, sides, etc. etc. I have accepted that as a given with any published and supported game-world. I'll prune the world as needed, pushing what I don't need into the background.
Magic-as-technology: Eberron embraces this concept with great gusto. Warforged, airships, the lightning rail and elemental galleons, alchemy and through it all, the artificer class.
The Magic Economy: D&D 4th ed. went most of the way here, with solid game-mechanics driving the value of items. With rituals and their components, a society has real advantages in standard of living. Eberron adds the dragonshards, which I'm going to run with and bring to prominence. Speculators aren't gambling everything to find a vein of gold or iron, but instead for an untapped field of shards, which can be the foundation of economic and military power.
Racial Issues: the elves-good, orcs-bad standards have always been my windmills to tilt at. Eberron gray areas to spare here, with the goblins of Dargunn and the marginalized shifters and the hated changelings. Human-vs-human conflict in the Last War is the great crime hanging over the world, as it should be.
Disaster: The Mourning, while not world-girdling, has big mysterious implications that can drive the campaign in whole or in part and give epic significance to the story (when needed).
Civilization: I need there to be decent, hardworking people, safety, arts and culture in my world. Unrelenting bleakness doesn't work with my story, I need the contrast. The Five Nations, and others like Zilargo are stable nations with borders and differences.