This video posted by KillerTravis in the ME 3 specific thread, shows the Bioware Marketting guy demonstrating switching the game to GamePad only play! This is the most anticipated feature of the Wii U for me as I sometimes don't get to have the TV when I want.
Footage is here
The part about the "Off TV Play" starts about 5:33
This feature has sealed the deal for me.
EDIT: Changed link to original source (GotGame)