Some video games can be good for the players. Some teach skills or information.
Playing games for too long has been shown to correlate with weight gain. And there may be better things you can be doing with your time. Some video games may also contribute to repetitive motion injuries, like carpel tunnel syndrome.
Playing video games should not be harmful, as long as you don't overdo it, and don't try to reenact the more violent aspects in real life.