All of that campaign playing took up 13.5 million hours of gameplay; however, War Games was actually the most popular game mode, with four million users clocking 16 million hours of competitive multiplayer within the first five days of launching. 1.9 million hours were spent playing Spartan Ops, Halo 4's ongoing episodic co-op mode.
And if you're wondering just how much overall death Halo 4 has caused, 343 says that 4,590,416,285 kills took place in all of the game modes within the tracked five-day period. That's over 4.5 billion kills, between fellow players, the Covenant, and the new Prometheans. With all of that killing, it's no wonder the planet is called Requiem.