As an artist, I can say "yes, it is". there are a lot of arguments as to why it's not, mostly they boil down to "it's violent". or "you just shoot things, it's all about reactions, how's that art"?
but lets look at it this way... LOTS of famous works of art are very violent. very! everything from roman to renaissance has lots of gore and death, yet, it's art. why? how? well, because it is. COD, while being a violent game, still has all the elements of any other work of art... but the genre of FPS is just different. it has its own way of story telling, its own way of immersion, and all of that just makes it a different kind of art.
it's just that, because of the nature of the game, we as a society (read: uptight and prudish) have tried to separate ourselves from anything that's even slightly controversial. look back in art history... anything not mainstream or that was controversial, was called out as "not art", yet, 10s, 100s, 1000s of years later, what do we study it as? well... art!
give it time... interactive media, including FPS or fighting games, will one day be recognized for the artworks they are. probably not in our lifetimes, but who knows, maybe our kids won't be so closeminded.
that said, I think there is a bit of discrepancy between the terms "high art" and "art". I think people confuse the two. I mean, when you hear the word "art", you think of works by Michelangelo or Picasso or Degas... but not the logo for Starbucks or heck, whatever's on your desktop wallpaper at the moment. despite my hatred for the term "high art", I think that's what most people are trying to render COD as, rather than the general term of "art". I hope that made sense. just cause something isn't the Mona Lisa, doesn't mean it's not art!