How does computer games affect teenagers these days?

I feel that its okay to play computer games occasionally. Some computer games help you to gain more it skills and trains ur vigilancy.However, most computer games are bad for our mind,eg.Wolfteam..Counterstrike..Gunz The Duel..and etcetra..Honestly, i also play these games but not as excessively as when it was december holidays.These games deteriorate our brain and "attract" us thus making us addicted to them.It is seriously not beneficial for us although it has the excitement :P I myself was once addicted to these games and scored real badly for my exams :( In overall, games can be good to us to distress if we play it with limits.