Super Smash Bros 4 for the 3DS. You were all thinking it. Here are the things I would like from it.
They should totally include the tunes from the Pokemon Trading Card Game. Yes, there were only four, but they were so awesome, that wouldn't really matter.
A more fleshed-out and coherent story mode. With dialogue, even (or rather, preferably) if it's just text.
EVERY STAGE, FIGHTER AND MUSIC TRACK FROM EVERY SUPER SMASH BROS EVER!
They could make room for it by cutting out all the trophy and sticker bullshit, pardon my French.
Now that I have covered my major points, I'll move onto other requests.
An OPEN-WORLD SANDBOX Mario platformer. Yes, it's sort of a step down from Galaxy, but it's a truly unique concept that hasn't been done before. No, I'm not talking about RPG gameplay, I'm talking about the runny-jumpy-wahey platforming and optional story that MADE GALAXY AWESOME! A game where all 120 stars can be found on the hub world as big as the USA. Obviously not THE USA, but you know what I'm talking about.
LOCALIZE THE MOTHER SERIES! Everyone wants an english translation, and if you don't give us that, Nintendo, you're just shrinking your money pile.