HardwareHeaven.com posted a review on Call of Duty: Black Ops 2 - The State of Call of Duty

Over the last decade Infinity Ward built the Call of Duty franchise to be one of the biggest in history, and the most critically acclaimed. This should have been no surprise given their previous success with Medal of Honor: Allied Assault. Infinity Ward continued their success story with Call of Duty 2 but when the third game in the franchise was in development it was Treyarch who brought the game to market, allowing Infinity Ward to freshen up the franchise soon after with Modern Warfare. Modern Warfare was the brands first move away from a World War 2 setting and allowed much more creative freedom which assisted in keeping critical acclaim high.

This dual development method continued within Activision with Infinity Ward and Treyarch alternating the development duties. A move which saw a yearly release schedule for the next installment of each game... but not necessarily the same level of praise with each.

  Call of Duty: Black Ops 2 - The State of Call of Duty