The Wii U's controller is the future. Okay, the idea of playing an entire game on its overly large screen whilst someone else uses the TV is gimmicky and largely unnecessary (not to mention the fact that it limits the console to the use of one and only one of these controllers), but the potential for a controller with an embedded hi-res touch screen is phenomenal.
There's the obvious stuff, like the ability to manage your inventory or view a streaming map & update waypoints etc without having to pause your game, but there's other stuff, too. Take Mass Effect & Dragon Age, for example. I don't know about you, but I sure do find it annoying to have to pop up that wheel and effectively pause my game to use powers/abilities/items. With a touch screen right there, you wouldn't have to. They could all be there, mapped out on little individual icons, usable with a single tap on a control pad that doesn't need to have a bajillion buttons. And the positioning of those icons could be entirely customisable. Hell the size of them could be customisable, too. God only knows how fantastic all of this interface potential could be if applied to the likes of Skyrim.
And then there's the potential for genuinely innovative gameplay enhancement, too. What if, in Deus Ex: Human Revolution, you had the ability to view hacked cameras through the controller? Not while standing in front of a terminal or in a little picture-in-picture box, but on a screen in your hands, while you continued to play the game on the TV. You could jump from camera to camera, checking the areas around you. Remember the Sightjacking mechanic in Siren? Where you could temporarily get a peak at the world through an enemy's eyes to help figure out the locations of your enemies and the dangers of the area? Same thing.
In FPS/TPS games, this thing do anything from allowing the viewing & piloting of a UAV or even a sniper rifle scope, all while the player can still see their surroundings somewhat on the TV.
In racing games it could be map, a display of stats, a rear view mirror or all three.
And let's not ignore its potential for a revival of the space-combat or mech warfare sim. How great would it be to be able to look out of the cockpit on the TV screen, and have your targeting computer, power readings and radar in your hands? Remember that enormous controller with countless switches and buttons made necessary by all the functions of your mech in Steel Battalion? They could all be there, on that screen, customised to your liking.
It's easy to dismiss this huge controller as Nintendo's latest gimmick, and hey - maybe all it'll ever be used for is gimmicky stuff, who knows. But its potential is enormous. It is the future of gaming, and gaming would be a lot better off if we realise it quickly.