In my first character tutorial we was asked to take a game that already exists and change the platform it for and make it suit a different one. The game I picked was Skyrim and the platform I pick to change it to was a iphone app.
So you would start the app and pick a character. You would then get the map of Skyrim and you would be able to travel anywhere on the map like you can in Skyrim. Once you pick a location the app would bring up a bunch of missions you could select from. Each mission would have a recommended level, if you meet this level or you are higher then it your character will have a 100% completion rate, where as if your character is a lower lvl you could lose the mission. If you complete the mission you will get both XP and items, whereas if you lose then your character will either lose XP or lose items. With the items you collect you can build weapons and armor to help improve your characters stats. With both crafting and doing missions there would be a wait timer, depending on how hard the mission is and the level of item you are crafting would effect the wait timer. You would be able to do a mission while you are waiting for something to craft but you would only be able to do one mission at a time.
I think that Skyrim fans would find this game fun as it would be the same sort of stuff they have seen before.