Been said above but a well fleshed out and generic-Ish setting would be great. Runequest has always had hundreds of what felt like novelty campaign worlds ("this setting is a realistic look at the Hittite empire" or "this is a 18th century setting meets silence of the lambs!") but precious few gateway settings for me to lure people away from pathfinder and dungeons and dragons.
While I love all the unique stuff my players like dusty tombs, flagons of mead, dragons, loot and all the other trappings. I can sell them on a hook or theme to a campaign such as the world is cold, old, at war, etc but any more and they get grumpy...
Basically a legend version of greyhawk, forgotten realms etc NOT another realistic setting or tekumel.