OK - just to let you know I am a behavioural neuroscientist who was part of the first team to explore whether cocaine activated same circuits as natural rewards (it does). As was posted above, gaming does change brain chemistry and activity in brain reward circuits, and these circuits are also affected by addictive drugs. The problem is that those same circuits are also activated by healthy, natural rewards and we simply do not know enough yet to be able to determine whether such activation is likely to lead to addiction. What we do know is that there is a well-financed gaming industry that pours R&D money into formulating games that are irresistible - just like the gambling industry. We also know that some people engage in gaming to the point that it harms their social life and their health. I suspect in the end we'll find gaming is like drug addiction in that there will be some people who are vulnerable to forming a compulsive, maladaptive habit.
Certainly I have seen that in some of the young adult male members of my extended family, who because of gaming have problems forming and keeping long-term relationships, have low professional/academic success because they're up into the wee hours of the morning playing games and walk around sleep-deprived all day, have problems setting priorities with their finances because the spend so much money on games, and who actually seem to suffer psychological withdrawal symptoms if they're not online every few hours. Are they happy? Not really....
The APA are currently revising their diagnostic manual, which is pretty much the definitive source on psychiatric and psychological disorders. The have specifically excluded gaming addiction for the next revision, but that decision is being challenged.
