We just met and this is crazy; but here's a Wii U, so play SiNG maybe?
SiNG was probably the moment during Nintendo's press conference where die-hard fans had their second biggest face palm (right after the Nintendo Land fireworks). To the naked eye, SiNG is a silly karaoke game with the gimmick of giving the lead singer the Game Pad so they can read the lyrics there instead of the TV. And, to be honest, that is exactly what SiNG is, but I wouldn't call that a bad thing in any way, shape, or form.
The singer can hold the Game Pad horizontal or vertically and then follow the Game Pad for instructions. There's no interaction outside of the singing, but in addition to the words, the singer also gets directions to give out to the crowd. It's pithy stuff like "Everybody dance!" to, you know, encourage people to dance. There are even some lines that the game encourages you to "let the crowd sing."
The crowd gets to watch the action on the screen, where lyrics are presented in a stylistic manner. They also can don Wii Remotes to dance along with the game. It's sort of like Just Dance in that regard, except there is no scoring in this mode.
That's the one thing that makes SiNG less of a game and more of a karaoke application: there is no game to it as of now. The Nintendo representatives had nothing else to add about the game, but the only modes shown were a Party Mode (for partying, naturally) and a Sing Mode, which is a single-player experience.
SiNG will be out around Wii U's launch later this year, so I guess we will have to wait until then to see if it'll be more of a game.