The game's first five days saw over 3,500 years of playtime.
In 1570 BCE, the adversarial Hyksos ruled Egypt, leaving the kingdom in disarray for the next twenty years. I bring this up only because that period was about 3,582 years ago - the same amount of time gamers spent playing Halo 4 in its first five days. While the Egyptians wouldn't have accomplished much if they had holed up playing donkey-powered, stone-carved Xboxes instead of retaking their country, modern gamers have already racked up an impressive number of in-game accomplishments: 31.4 million hours played, and over 4 billion kills.
Halo Waypoint, Halo 4's official community site, has tracked metrics since the game launched. The bottom line is that a lot of people have been playing Halo 4 since its November 6 release - over 4 million, to be somewhat precise. The game's campaign has occupied 13.5 million hours for them, although multiplayer still comes out on top with 17.9 million hours logged. Over one-fourth of players completed the campaign, and 6% even managed to do so on Legendary difficulty. These numbers, however, are all small potatoes compared to the total number of kills: 4,590,416,285. In other words, if Halo 4's mortality figures translated into real life, the world's population would decrease by over half in less than a week.
Along with some pretty impressive sales figures, Halo 4 seems to have grabbed the fanbase's attention (and time) as effectively as the previous entries in the series. These "first five days" figures are unlikely to continue over the long term, but chances are that by time they taper off, Halo 5 will be just about ready to ship.
Source: Halo Waypoint