Most games have off tv play which is pretty darn useful,then there is the NFC for Amiibo, which most people seem to forget, so that's one success the gamepad can be atributed toward. Here are a list of games I think utilize the gamepad in cool ways as well for good measure.
Nintendoland
Mario Party 10
Windwaker-(nothing special, but item management is so streamlined and effortless)
Deus Ex
Need for Speed U
Game and Wario
Batman arkham city
Splatoon
Wonderful 101
Zombi U
Lego City Undercover
Captain Toad
Kirby Rainbow paintbrush
Affordable Space Adventures
Art academy
Wii Party U
As you can see, the gamepad is reasonably well represented. I think its a good innovation that I have personally enjoyed but hasn't captured the minds of the mainstream.
