The Kinect plays a much more integral part in the gaming experience, not like the half baked keep Mum fit thing that it is at the minute.
The sensitivity of it is massively increased, it can sense facial expression change so it can see what scares you and instruct the Xbox to use the information accordingly to influence game A.I. , it also sense's changes in body attitude so it can see you twist your wrist and adjust the throttle on a bike game, or move your finger in a sniper game. It will also work in the dark now, and the cack handed nature of the original kinect in regards to placement, room size etc is all gone, just turn it on and use it now :-)
It really is a step forward, there is loads more this thing can do, however if you dont want to use the kinect, unplug it. However from the video's and the seminar that the chap gave, you really will be taking away from the gameplay in some games massively.