Well, what can I say, the game hasn't changed it's formula in 6 years, so I doubt they will change it for any future game in the franchise, sure they can change the setting and time periods, but in the end it's the same mindless killing game that has been dumbed down over the years so that "Casual" gamers can play it.
Nobody ever cares about the story in CoD, they usually just go through it once then hit the Multiplayer, but I'll lay down on outline for the typical CoD story; you usually first start off in a base, where they teach you the basics of ADS and throwing grenades, then they send you to find intel on an enemy base, camp, or personel, then you fight through a few streets and buildings until you reach your objective, completed mission, sends you on another one where you have to identify a target of importance, but something always goes wrong and you end up fighting for your life, just to be captured and tortured for a while till they either kill you or you get rescued, then you proceed to either a sniper mission, vehicle mission, soldier mission or a mix of the three, up until you fight one final mission that ends in someone with a knife in chest or in a explosion of some sort. That's a typical CoD story in a nutshell.
The graphics are pretty good, to a degree, the textures and other details sometimes look like the developers didn't really care about them too much.
The audio isn't the greatest, the weapons sound pretty bad compared to the real life sounds, voice acting is off at some times, but other than that, its alright.
The gameplay, the one part that ties every CoD with future CoD's, if you have played one CoD, you literally played them all, the only difference's are the guns and time settings, everything else is the same.
Multiplayer, the bread and butter of the CoD franchise, they have only added a few little tiny details here and there in the ENTIRE series, if you play CoD only for their Multiplayer, you purchase the same game year after year after year, for only a handful of new gizmos, gadgets and features.
Also I should mention, Treyarch do provide innovations to the series, first was in World at War with a simple "Nazi Zombies" game mode, simple fun for you and 3 friends to work together to survive a zombie apocalypse, next on Black Ops, they added a "Dolphin Dive" to avoid oncoming fire and "Cod Points", to unlock whatever weapons you want and their attachments/camos, as well as perks, all while improving the Zombie experience with more interavtive maps and secrets to keep players entertained even to this day.
These games have been released every year for the past 6 years, it has always been the same game, just simply repackaged with a "NEW" sticker slapped on the redesigned cover, sold to the people who generally want to believe that it is something new and refreshing, only to find disappointment.
FINAL VERDICT: Rent