The gamepad isn't that big of a deal, for someone that has a family? Have you ever played a game with your kids and realized that finding a compromise for making the game as challenging for you and the kids is almost impossible? Watching some Nintendo Land games and the new Super Mario Bros. demonstrated that the additional gamepad can easily break down that barrier. The idea of having to keeping the kids alive in Super Mario Bros. by placing platforms under em can be very challenging in itself. Rayman Legends also comes to mind in this regard with being a helpful sprite, or doing the opposite and letting the kid be your helper. The concept of babysitting in a game is often an awful experience dealing with AI NPCs, but when it comes with doing the same thing for your own children, it's a blast. The Wii U just makes the whole capacity of being an administrator or dungeon master in a game all that more appealing and feasible.
You can cry about Nintendo losing its touch with the demographic it was aiming to please with the Wii, but giving me more power over how a game plays out for both me and the little fellas is exactly what I'm interested in. And look, I don't even have to sacrifice a player slot to do it; the kids can have their friend over and I can still be involved!