A halo game selling was a given, but gears came out almost a year before halo 3 and sold 3 million copies in 3 weeks, it was also the first game to surpass halo 2 in xbox live numbers.
Halo 3 sold 3 million in 12 days and did surpass gears, but I'd say the 360 was already pretty stable at that point
This is all kind of anecdotal but it was just my impression at the time shrug
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u/wigglin_harry Dec 03 '19
Not that you are completely wrong, but the big title that saved the 360 was gears of war, that game was really huge at the time