I wouldn't call CoD (past 4) "changing it up". They took their standard WW2 shooter and changed the textures on the guns to make them look modern... and that's about it.
In my mind "changing it up" would be... like Bulletstorm, where most of the weapons are completely unique, it added a lot of mechanics and there's more to the gameplay than "center screen on what you want dead and press a button".