.. that would be Halo 3, which I dutifully posted in "Halo 3 Launches"
How big?
Well, as I stated in that post, US$170 million big. This compares to:
Connor has graciously returned my PC copy of the first Halo to me; I will be installing it just as soon as I finish "Starcraft, Brood War".
Yes: I'm that far behind.