I think like anything it can lead to sin. But in itself it is not one. Not that I want to use the "Its just pixels on a screen" excuse but these are games. Not humans we are sinning against. Although if your playing multiplayer, then you are actually sinning when you swear at the other player.
And lets not forget age makes a difference. FOr example I recently beat Fallout Vegas. In it you can make all kinds of decisions. Such as being nice to someone, or stealing from them or even blowing their head off and stealing what you need. No matter the choice, as adults I think we mostly recognize its a game and don't simulate it in real life (unless we have a mental condition).
Where as a kid playing it may know what right or wrong is, but in the real world will not always distinguish after a while about making a bad choice in real life vs the virtual world. WHich is why I don't like kids playing adult rated games.
Actually a recent study confirmed something I've been saying for years. Thats our brains don't fully mature until around 25. Its why when we yell at teens for making stupid decisions, they aren't making them on purpose to rebel always. That part of the brain isn't fully matured yet. They think of the here and now such as "Did that guy just call me a name?" (shoots the guy). Where as adults we think of long term and consequences.
Its why we see more and more kids killing kids. And young adults killing young adults. There brains aren't ready yet for the stuff they see in games. As much as I used to say each person has to decide for themselves, I don't think if I was 22 I should trust my view on if I am ready for a game because the here and now side of me at that age would only care about playing the game at that moment. NOt the long term affects after.