This is a HUGE plus for me, in fact, it may be one of the main things I look for in a girlfriend (not saying that if she doesn't like games then I'd reject her, it's just a major plus if she does like them). I love it when my friends have common interests, and if my girlfriend has an interest in my favorite hobby, then that's just awesome
However, I like it even more when they don't really play video games, but are willing to learn. While I don't like to brag, I consider myself really knowledgeable in video games, so a situation like this will give me a chance to be the master, a teacher who shows someone the ropes and basics, then move on up until she's able to hold her own against anyone. I've never ACTUALLY experienced this, but I'd love to someday