If Halo 4's sales pattern continues, it is expected to sell through approximately 4 million units by the end of the week. That would top the 3.8 million units sold worldwide for Halo 3, and the 3.7 million for Halo: Reach. Looking back further, Halo 2 sold through 2.4 million units on its first day of availability.
When you look at the bigger picture, Halo 4's numbers could have been much, much higher. Activision's Call of Duty: Modern Warfare 3, the current record holder for the biggest video game launch day ever, selling through 14 million total units its first week, 7.5 million of which were on Xbox 360. That equates to at least 3.5 million Call of Duty buyers whom have chosen to skip Halo 4, at least for now.
Positive word-of-mouth could help propel Halo 4 sales through the holiday season at a stronger pace than its predecessors. Reaction from critics (read our Halo 4 review) and players has been mostly positive. Potential buyers sitting on the fence fearing "yet another Halo game" may be swayed into a purchase.
We're waiting for Microsoft to send out an official press release regarding Halo 4's launch to see how their numbers compare.