Love Rayman Legends, it's awesome, beatiful graphis, great controls and replay value!

I want to have Darksiders II, because I read only good reviews for it!

Black Ops 2, Amazing Online MP and superior graphic on gamepad lol.
Monster Hunter 3 Ultimate, Fantastic game and I played for almost 700 hours with a lot of my new and old friends all around the world.

Gameplay

Monster Hunter 3 Ultimate. The brilliantly gritty, risk-reward based combat system making every encounter a thrill.

Technical/implementation details

Trine 2: Director's Cut, for actually using Wii U's extra horsepower to make an already gorgeous game even prettier. Need for Speed Most Wanted U gets an honourable mention also; it's not as beautiful as Trine, but at least it's an upgrade over PS3/360.

the effect it has had on you or your friends

Need for Speed. They were impressed by how good it looked.

any lessons for devs and/or Nintendo if any

Nintendo should learn from Criterion and Frozenbyte, and at least try to push the hardware, if only to disprove misconceptions in the gaming community about Wii U being weaker than or on par with PS3/360.

Rayman Legends, even though I have plenty of 3rd party Wii U games I don't think I've beaten any except for this, but this one was awesome. I also have ZombiU, MH3U, ACIII, CoD Ghosts, and I intend to get ACIV, Darksiders II, and more, but not until I get the time to actually play them XD

Rayman definitely made great use of the Wii U gamepad and with the other versions not having the features or them just not being as convenient (GamePad as a 2nd-screen is included/a mandatory part of the system) or whatever, I can't imagine the other versions being as good. XP

^also I think you maaay have misinterpreted the original post though it's not a big deal (and SM3DW isn't 3rd-party but whatevz haha)

Fixed the third party issue. I actually have no one  game that fits all the criteria well so I decided to split it.

Mine is probably tied between Sonic Lost World and Deus Ex HR DC.

ZombiU by a country mile. Goes back to the days of the very first Resident Evil where even ONE zombie can be a threat to your life. The Nursery still gives me nightmares lol

Everybody ignoring how The Wonderful 101 uses the Gamepad in almost all possible ways? That game was awesome.

Rayman Legends, no question.
Gameplay, graphics, sound, GamePad-use, 5-player asymmetrical multiplayer... Everything was done very well.

@HintHRO: TW101 is published by Ninendo. And yes, it is awesome! It was my favourite Wii U game until 3D World was released.

Wow I own 11 full retail games for the Wii U 9 of them is third party titles. I would have to go with either Batman: Arkham City Armored Edition or the one I recently bought Assassins Creed 4 Black Flag.(Or both they are both excellent games) my third choice would be Ninja Gaiden 3: Razor's Edge. That is awesome.