ZombiU has an asymmetric multiplayer mode, where one player uses the Wii-mote/Nunchuck or Pro Controller, and tries to survive, while another player uses the Gamepad as a means of deploying zombies to try and take out the other player. That's pretty fun.
New Super Mario Bros U and New Super Luigi U both have touchpad-only parts, that players with the Wiimote/Nunchuck or Pro Controller won't be able to do. It's not necessary to complete the game, however, it does add another option for another player to either help or hinder the other players. So there's that.
Rayman Legends has a similar feature as New Super Mario Bros U and New Super Luigi U, however, it's actually required to complete the game. Whether playing singleplayer or multiplayer, the gamepad touch screen parts are mandatory to progress in the game. So that might be more up your alley, in terms of playing asymmetrically, as co-op play can have one person control all of the mandatory touchscreen parts while the other person can use the controllers to traverse through the levels.
Need For Speed: Most Wanted U made it so that if you are playing solo on the Gamepad (whether on tv or on the gamepad itself), you can push buttons on the touchscreen to change things like the traffic cars on the road or the day/night cycle, or things like that. You can even turn the cops off, and they'll disappear and stop chasing you. So there's that. Or, you can play with the Pro Controller, and let somebody else have the gamepad, and they can randomly change the options while you are playing, not knowing what they are going to press. You can be in a police chase, and they can either add traffic, to try and screw you, or take traffic away, making it easier for you to get away. It's more of a novelty effect than asymmetric play, really.
I think of all of the asymmetrical gameplay on the Wii U, ZombiU probably did it the best, other than NintendoLand. However, Wario's Game and Watch and Rabbids Land both have asymmetrical multiplayer minigames. Not all of them, but some of them. So there's that.
It's not used as much as it can be used. I think games that are exclusive to the Wii U are more likely to get that style of play. Games that are multiplatform most likely won't even bother to try anything like that. Rayman Legends did, but it was originally an exclusive title. However, games like that may add the asymmetrical play as an add on, and not really build the game or mode around that. There's currently not a whole lot of games that use this feature. But like I said, ZombiU and NintendoLand are probably the two best in terms of that feature. With Rayman Legends and Mario/Luigi and the minigame games adding their parts in to.
