It looks like you're new here. If you want to get involved, click one of these buttons!
In my recent course of basic Buddhist concepts at the local Tibetan centre (Gelug), the monk was explaining karma and he said, "even intense thoughts can leave a karmic imprint". Now it occurs to me that computer games generate pretty intense thoughts and emotions, and so may well generate karma, but they also include actions. You are actually killing your on screen opponent, albeit by pushing a button rather than hewing him in twain with a broadsword as our distant ancestors might have done.
From that standpoint, computer games are going to generate between a little and quite a lot of negative karma. You may be killing non-player creatures in the game, things that look non-human, or you may be killing very accurately displayed characters representing actual human players. You may be very "into the game" or you may be very detached and treat it as just pixels. All of which is besides the fact that greed and treasure are big motives in most games.
Certainly food for though... what's your opinion? Do you even believe in karma?