There are games and there are games. And my guess is that games that map onto the real world more closely may have more intrusive effects than others. How could PacMan realistically affect real world functioning? You are guiding a blob of pixels around a maze, there are no real world corollaries to this. However, interacting with with photo realistic others in simulated environments could have a very positive impact. Take as an example some vulnerable kids who have learned to deal with others with aggression, then expose them to a simulated where game play success is only achieved through appropriate interactions, we might see positive effects in real world behaviour. At least this is the thinking of some developmental behavioural scientists... whose names and work I cannot at the moment find.