The Wonderful 101, but if I have to choose from the poll, then it's Pikmin 3.

Windwaker hd

Technically ZombiU has multiplayer as well, but then so does Bayonetta 2, Xenoblade X, and Pikmin 3. ;)

Super Mario 3D World

While I would agree with most people here, Xenoblade X and Bayo 2 are the top picks, I HAVE to give some credit to Fatal Frame V. TONS of content, multiple endings for every character, side missions which involve you learning about how certain ghosts died on the mountain which earns the player lenses, large areas to explore, tons of cutscenes through soul glances, intriguing story, and great atmosphere. If you can get past the fact the characters move awkward it's definitely a top pick.

Fatal Frame/Project Zero 5

What about Assassins Creed 3 & 4? windwaker HD etc etc etc

Bayo 2 and Donkey Kong are my favorites.

And I adored ZombiU while playing it. It definitely had flaws but I had a ton of fun playing it. Still the best use of the Gamepad to date for me personally.

Bayonetta 2 hands down.