Red Dead Redemption style sandbox + Indiana Jones globetrotting adventure.
Each region would be a different country.
There'd be horses, motorcycles, jeeps, boats.
Main story missions and then side quests for hunting smaller treasures using puzzle-related maps.
Euphoria powered animation and physics.
Some action set pieces would of course be scripted, but SO MANY would be created by US the player!
Exploration would be amazing.