Games and interactive systems are different from any other medium in that they require their users to constantly make decisions.
The decisions' type and the intensity of interaction define the global experience.
These two elements form the TIMT (The Interaction Mapping Tool). A tool that will help you quantify the user experience of any interactive activity and adjust it's variables properly to fit your users' state of mind.
Granted, you will not look at interactive media the same after this talk.