Neonchameleon
Legend
When I started my current campaign, using what started life as my ten level 4e retroclone, I gave the players a choice of "party character sheet" to determine the campaign style. I presented them with three; the Stonetop based Settling On The Borderlands, the Pirate's Life, and the mercenary Band of Bravos. They picked the Bravos - which let each of them write a different objective or enemy group. The vampire PC picked a master vampire and wants freedom and to kill their maker, the dwarf wanted to rescue his family black sheep brother, the Eladrin's in trouble with the Fey court, the Barbarian's on the outs with his own tribes, and more. It's not the best mapped world but the entire thing has been a blast with the characters tied to the world, and the NPCs and plots are frequently ones I wouldn't have thought of without the players having initially set up the threats.