This question is not off-topic. It is asking if a particular action is a sin, and the question which actions are sinful is relevant to Hinduism. Just because the question has the words "video games" in it does not make it off-topic.
This question is very relevant today since many people play first-person shooters. For example, according to this article, an 8 year old boy likes Call of Duty because of the killing:
"I love that game! I LOVE IT SO MUCH," said the eight-year-old. I asked him what he liked about it. "The killing..." he said, in a sing-song, matter-of-fact tone.
My pet theory is that since it's the Kali Yuga, many people have Rakshasa and Paisacha tendencies and enjoy killing people for fun and satisfy that desire through violent video games.