Ambinder stated that the biometric feedback includes the use of a player’s sweat, calmness and eye motion, which has resulted in a variant of Portal 2 in which the game can be controlled via eye movement, which is apparently a lot quicker than reacting with your hands. The sweat and calmness gauge is also being used to determine within a game of Left 4 Dead, how much time is required to complete an objective.
Of course we don’t expect Valve to be releasing these games anytime soon with their biometric modifications, but it is interesting and awesome that a game company is looking beyond designing a new game in terms of features and story, but how a player interacts with it as well.