at first it should not be like mario sunshine
2)they need to keep up the quality of mario galaxy-main problem here:less developing time but far more ressources/staff is needed as HD needs lots of more manpower than SD
3)some attractive use for the controller.As long sd the useadds nothing special and attractive casual gamers won't be interessted and won't buy a wii u just for one game.
Some core gamers may do the same:rent game and console for 5 days and give it back after finishing the game
4)Galaxy2 isn't that old,3ds mario is pretty new,maybe a new 3d mario could cause the same fatigue problem mario 2d has on wii u
and i think too many games are using the name mario and he is nothing special anymore







