How significantly has Call of Duty changed gaming?

Call of Duty will always have its detractors, but I'm proud to say that I'm not one of them. A franchise that has sold over 125 million units (and counting) and one with a fan base of players who have racked up a, frankly alarming, 1.6 billion hours of online play on Modern Warfare 3 alone, is bound to attract the ire of many. The series has become so rooted in console gaming lore that it is now impossible