For me it would have adventure elements like Uncharted or Tombraider but would include choosing and improving a character and have first person elements like Skyrim. I would go for a storyline based on I am Legion, and the adventure would be the search for a cure to a terrible disease taking place across the globe, with plucky sidekick Ben Green, who is gradually succumbing to the disease and needs regular treatments which have to be found along the journey in order to stop him turning, but if you take too long he turns and becomes an enemy that you have to bring back from the brink if you find a treatment. Eventually the game will be solved by finding a cure, probably in some underground bunker that was filled with scientists that managed to make a cure but didn't manage to save themselves in time.