It's Mario Maker for me.

Nes SMB
Snes ?
N64 SM64
GCN SSBM
Wii wii sports
WiiU splatoon

GB pokemon

GBA

DS

3DS 

What are the HHs? 

I'd say:

SNES: Super Mario Kart

GB: Tetris

GBA: Pokemon

DS: Nintendogs

3DS: Super Mario 3D Land

Splatoon could very well be the defining title for the Wii U, but I think Mario Kart 8 and Super Mario Maker could still make a claim for it too. It all depends on how history unfolds, even Smash and all of it's DLC and Amiibo line is still in contention.

There is no doubt, though, that Splatoon is a massive win for Nintendo and is at least as big as Goldeneye was for the N64. It's funny because I kind of grasped at straws this time last year and said that Splatoon might be Nintendo's equivalent of Portal and that it could become huge... I honestly never thought that this could actually be the case.

YES IT WILL!

Yes, I would say so

Yes it is. it really provided how cool to play a shooting game with the use of some motion controls.
The colors added coolness and avoid the same old shooter type games out there.

If Nintendo could have partnered with Activision about the motion controls with HD graphics for a COD game, i think it would sell in Wii U.

In the sense that Splatoon could have been the THE GAME, had it been there at launch, that could have made the Wii U a sales sensation. Yes.

Consoles are defined by their whole libraries, not a single game.

Hmm, it's quite possible. It is quite a nice big hit on the console, though I think it'll have to compete with Smash Bros and Mario Mario. Maybe even Zelda too. Those 2 games are also great. I think the Wii U will have a lot of great games to be remembered by xD