What do you look for in a setting?

[Prometheus]

1) A regular amount of magic: Low magic seems bound to either be a failure or have replacements that aren't as interesting. If you entire gaming group is power-gamers that cannot resist becoming Batman or Cheeseballs, play a different game
2) Powerful natural hazards: There is nothing more silly than a hazard like and Avalanche, Sandstorm, or Quicksand which utterly ineffective to higher level players. They make for fine challenge when level appropriate, but I think that it should be able to scale a little higher, which can mean outlandish but also interesting terrain. Correspondingly, creatures of the wilderness should present a threat even too adventurers, which makes travel for commoners difficult. Perhaps a "Forbidden Zone" as described by Alyosha.
3) Unique cities: A kingdom with either expansionist or defensiveness strategies gets boring real quick. Mix up the system of government, culture, landscape, races, classes, etc.
4)Unifying theme: There should be something that connects the entire landscape. Landlocked? In the process of colonization? Island chain? Epidemic disease? Dominant religion? Or yes, even Low-Magic...Think Dune. Think Waterworld. Think Post-apocalypse. Think Salem. It also serves as a major plot device and a n explanatory factor for all major world interaction.
5) Good DMing: Seems to be much more influential than setting :P