The following points were made by Ben Schachter of Macquarie Securities, who thinks Call of Duty may have peaked. Here are his reasons why.

HD hardware and software as a whole have been declining all year (i.e., it is not just weak Wii sales that are impacting the industry)
Lifetime unit sales of Modern Warfare 3 are slightly below Black Ops
The genre seems tired
The futursitic setting may not have the same appeal for some
The macro economic environment is causing some gamers to hold back on upgrades
Currency fluctuations mean that European sales are worth less to ATVI shareholders