Concept.
The Gamepad just can't be used in any meaningful way. Nintendoland was nice but aside from "asymmetric multiplayer" there's no reason for it to exist as a mandatory controller. Mario Bros. doesn't benefit from it, Pikmin 3 neither (Miyamoto himself said the best way to play the game is the Wiimote), Wind Waker would've been more exciting with a Wii remote control scheme, Donkey Kong can be played with any controller and Mario 3D World as well.
There's a few games that benefit from the gamepad but it's never a must-have. Offscreen play is nice but not a selling point. The gamepad also makes it hard for non-gamers to pick the console up and adds like $100 to the retail price. If something makes your product more complicated, expensive and bulked without adding value you should better drop it.







