What is the Wii U? The first thing you notice is that the system's controller is like a tablet computer that supplements the big image the Wii puts onto your TV. And what good is that? Well, the small screen is enough to keep the kids happy if they want to play with the Wii U while the grown ups are watching TV. In a few weeks, Nintendo will unveil software that also lets the second screen act as a souped up remote control for all the digital content, from music to movies.