He takes the freaks out first with a handgun, and then a lightning gun thing, and then some kind of powerful weapon capable of blasting a hole in a nearby apartment building revealing ... one freak repeatedly spanking another one. Humor!
But it's how you do all that shooting that's really interesting. You hold the WiiPad out in front of you, and move it physically around to turn your character and aim your weapon, with the pad's screen displaying your character's view. For those of you with 3DSes, these gyroscopic controls are like playing Face Raiders. It's an intriguing take on console FPS controls, but it's also a very physical one, requiring you to spin around constantly.
Multiplayer doesn't use that control system, but swaps it out for another neat use of the WiiPad. In the multiplayer mode shown on stage, one player used a Classic Controller Pro for a traditional FPS-type experience. But the other player, on the WiiPad, is presented with a top-down view of the map, and an inventory of various freaks to drop on the opponent. So while one player is experiencing an FPS with rapidly spawning enemies, the other one is playing a top-down action/strategy game about placing creatures in the right positions at the right times to overwhelm the poor guy on the street.
This is what's most interesting about the Wii U, in my opinion: the kind of experiences that allow for two players to interact with the same game, at the same time, in vastly different ways. Just try not to think of the fact that any game could do the same thing online, since each player has his or her own TV.