I'm on the fence with this, but as Portal 2 has elements of a first-person shooter, and that genre is tricky to adapt for Kinect, it looks like a breakthrough to me. Here someone has hacked Kinect, using FAAST (the Flexible Action and Articulated Skeleton Toolkit), to play Portal 2. Firing a portal is accomplished by extending one's arm 18 inches forward. Leaning and arm and leg gestures control movement and looking.
Kinect Hacked To Play Portal 2 [RipTen]