I'm not the all-knowledgable type, but there's definitely a certain "feel" for arena shooters (formula maybe?) that CoD doesn't comply with. Just look at the gameplay for either Quake/UT and then look at CoD. The only thing they have in sync is speed - of which CoD is still the slowest of the three by a considerable margin. Map designs, core gameplay mechanics (perks, item pickups, powerup), movement, and depth leaves CoD the odd man out when it comes to old-school arena style shooters. and even in the modern senseit falls behind something like Toxikk, Warsow, and the upcoming Reflex.
CoD is in its own category, which I like to call McDonalds FPS.
P.S. I love arena shooters.