I'll also like to recommend this quick and very sharp critique of the validity of recent reserch on video games and violence by Jeffrey Goldstein:
Young people bring their entertainment choices and experiences to bear on their intense concerns with questions of identity, belonging and independence. Nearly all their public behavior – the clothes they wear, the music they listen to, the rings in their noses, and the games they play – has a social purpose. Until researchers look, not at isolated individuals forced to play a video game for a few minutes as part of an experiment, but at game players as members of social groups, we are unlikely to come to terms with violent, or any other, entertainment.