It is a motion-controlled brawler with folks like Magneto, the Hulk, and Wolverine.
Avengers: Battle for Earth was not shown off for Wii U at E3 2012, but it was playable at the Microsoft booth. The Xbox 360 version only uses Kinect, but on Wii U, the game will use a variety of control schemes, including Wii U GamePad, and Wii Remote and Nunchuk. As the game is nearly identical in content to the Kinect version, the focus is on motion controls.

The demo for Kinect was showing off a versus mode featuring brawler combat from the third-person perspective. It reminded me of Ubisoft's Power Up Heroes, which came out on Kinect last year. Attacks are performed by making motions to simulate the moves. While the Kinect version features no controller, players will likely do similar motions using the various Wii U control options.
In addition to a versus mode, Avengers features a single-player campaign mode that is based off of the Secret Invasion comic story. The gameplay in the campaign is reminscent of a brawler, and features the same third-person view as the two-player versus mode.
While an official character list has not been revealed, the roster is being filled out by trailers and the demo. Captain America, Iron Man, the Hulk, Hawkeye, and Black Widow will be making appearances. Magneto, Wolverine, and Spider-Man will also be in the game, confirming that the game's scope includes the greater Marvel universe.
Avengers: Battle for Earth will come out on Wii U around the system's launch later this year.