Last year's Call of Duty: Black Ops and 2009's Call of Duty: Modern Warfare 2 both remained the most played video games on Xbox Live the week Battlefield 3 hit stores, according to Microsoft stats.
It's worth noting that Battlefield 3 wasn't released until Tuesday, Oct. 25 and that these numbers include Monday's players. So folks who may have abandoned Call of Duty for Battlefield on Tuesday in North America (and later in the week in Europe) may still be showing up for their gameplay on Monday. Next week will give us the first full apples to apples comparison.
Gears of War 3, when it hit, managed to squeeze between the two, often dominating Call of Duty games for a week on the charts but as of last week Epic's shooter has drifted down to the number four spot, beneath the Call of Duty duo and Battlefield 3.