An adventure with a nice switching of environment would be cool, you could switch between fabletown, the farm, homeworld, arabia/arabic fable town etc etc. It would also be a lot of fun to have more than one controlable fable, to add to more challenging puzzles. i.e. use the fables abilities to come up with solutions, it would also be fun to have more than one solution to a puzzle, say bigby would solve it differently than snowwhite for example. And than as finale some big ensemble solution to a big puzzle.
As for style I think you would have to go 'realistic' in appearance.