Adventure game would be sweet! With hand drawn backgrounds like Insecticide's concept art. I found them very Full Throttle-ish, Grim Fandang-ish. Love them.
A Grim Fandango 3d style of game would be nice too! With nice rendered backgrounds, and 3d characters. But not more than that, keep it classic. Didn't like Sam n' Max 3d animations, clumsy and un-flowing.