They sure did! They took things that everyone else was doing and then did them lots more than anyone else.

Well, in a lot of ways, CoD 4 really did have a huge impact on the FPS genre, the same way the iPhone had a huge impact on the phone market. Just compare and contrast the games before 2007 with the ones that came out after 2007 and you can see the influences. Before 2007 people were mostly playing shooters like Halo, Gears of War, Prey, Doom 3, Resistance: Fall of Man... after 2007 the modern-setting "realistic" shooters started popping up everywhere with similar mechanics and gunplay. The influences are very evident in, later Battlefield games, Homefront, Blacklight: Redemption, Medal of Honor, Bulletstorm, Crysis 2, and even Halo 4!