To the topic creator, to call Sunshine a must-have Mario game and then to dismiss 3D World is criminal. Having played both I consider the latter considerably better than the former. 3D World is so much more than just a 3D Land sequel, I thought the community had figured that out by now. Just buy the game and you'll see how must-have is - I promise you will not be disappointed.
NSMBU is not must-have, but you know what, it's the best NSMB game there is. Find time for it some day, especially if you can get it fairly cheap - I think it's a very overhated game, I had a lot of fun playing through it the last couple of weeks.
The Wii U does lack a Mario game (or any game for that matter) that hits the heights of the Galaxy duo. I hope one is in the pipeline, but who knows. For now my main hope of a game of that quality comes from Zelda rather than Mario.