One person in the party is evil and will try to secretly destroy the party, and the rest of the party knows that, but they don't know which one. Twist: Everyone's evil, and everyone thinks they are the sole evil one. Alternatively, nobody's evil, and they all drive themselves mad with paranoia.
You all play as (Since I'm assuming this is heavily influenced in D&D) cave-man barbarians who have been frozen in ice until modern day. Various hijinks until inevitable death. DM narrates in caveman speak. "You see man open up big shiny beetle and get inside. Beetle run off. What do?"
Hillbilly moonshining campaign.
Campaign run in reverse.