My employer, Christianity Today, posted an interesting and important editorial:  “Deadening the Heart: Killer video games are no 'safety valve'—quite the opposite.” Here’s an excerpt:

Good teachers know three things that contribute to effective learning: active participation, rehearsing behavioral sequences rather than discrete acts, and repetition, repetition, repetition. Video games employ all three. In addition, the vast majority of the gaming scenarios (like the random killing of prostitutes) fail to show the real-life consequences of violence. Perpetrators go unpunished. In short, violent games can deaden us to the horror of violence and stimulate our native sinfulness. It shouldn't surprise us that all media shape us, which is one reason Paul exhorts us to think on things that are true, honorable, pure, lovely, commendable, and excellent (Phil. 4).

Some say these are just games, and that we shouldn't take them