My thoughts on the subject, since its already come this far (and I'm well aware of the irony of what I'm about to say):
I am a firm believer in choice. Above all else, people should be free to make their own choices about what they do, what they say, and how the act. However, I also believe in accepting responsibility for the consequences and that certain liberties can be limited due to the choice of the people to do so, that is to say democracy.
In addition, I also believe that everyone is entitled to their opinion, which includes the ability to be offended by an opposing opinion. If we, as a collective people, begin to eliminate peoples' opinions by limiting their ability to make choices counter to our desires, then we are doing everyone a disservice. It is a good thing that some topic/word/political outlook/racial remark offends you - that means you still care about something. However, it is not acceptable to use the fact that you are offended to justify limiting others' liberty.
That said, the issue in question is the usage of "God" (or "G-d" if you're of the Jewish tradition) in a video game. You find this offensive because its counter to your religious beliefs, specifically the commandment that you shall not use the lord's name in vain. That actually stems from the archaic practice of the Egyptians prior to the exodus of the Jews, where the Egyptians would command their gods to do something ("Hathor, just as you sheltered Isis and her son during their journey, so shall you shelter and protect my children", etc), but I digress. I find it perfectly acceptable that you are offended by this, just as I understand why some are upset by racial slurs. Yet a) that is just your opinion, not the opinion of everyone else, nor an opinion which the majority holds as important enough to protect, b) you are not forced to participate in any of this, though it is regrettable the valve did not put a content filter in place like many other games have done (fyi, avoid mmos) and c) the games in question are rated M, partly due to language, which I am assuming phrases like "god damnit zoey" are part of the reason for, since no E game would include that (L4D -"Blood and Gore, Intense Violence, Language", HL2 - "Blood and Gore, Intense Violence", HL2 Ep.1 /2 - " Blood and Gore, Intense Violence, Language").
The moral of the story is this: If you are so worried about opinions that contradict or oppose your own, or you do not wish to ever debate the issue, then you essentially want to live in a plastic bubble where everyone is your form of politically correct. Otherwise you should understand that we are not all the same, nor do we all hold anywhere close to the same beliefs, and the exposure to different ideas and view points is part of what makes life so unique.