I grew up addicted to video games. I liked to spend all my weekends at my local internet cafe playing world of warcraft, counter strike, and etc...but it never affected me in a negative way, well i'm still addicted to video games and i haven't recieved any negative effects. so i think it depends on how mature and how old the child/teen is.
only negative affect i got from videogames is the compulsion to jump on turtles when i go into a pet store
and ive yet to run around the mall with a weapons killing people (Mind you, ive seen middle-aged women almost kill people in the mall around Christmas time, so maybe they were playing dead rising before going shopping )