Call of Duty is the largest First Person Shooter franchise of all time but two of the biggest instalments (MW 2/3) in the series just seem stale and its likely that the next one (MW4) will follow this pattern. In this post I will suggest changes that mainly apply to the Modern Warfare series as I feel Treyarch saved the franchise with the changes made to Blops 2. Although I do feel some of these apply to that game as well.
The best thing about Black Ops 2 was its story. It was engaging, featured multiple endings and has one of the best video game villains of all time. The Modern Warfare games on the other hand feature ridiculous stories that can be hard to follow and just aren't entertaining. Modern Warfare should follow Treyarch's example and Treyarch should carry on down their current path and develop their ideas.
Destruction and Vehicles
One of the big reasons I think Battlefield has the better multiplayer mode is that it features vehicles and the environment can be destroyed. Couple this with the awesome sound and you really feel the fight. Call of Duty has good multiplayer but by taking taking a leaf out of Battlefield's book it could really shine. Treyarch already changed it to be more team based so now it just needs to up the intensity.
A New Graphics Engine
The graphics in Call of Duty aren't as bad as haters like to make out because the engine is tweaked from game to game but what would be really great is if the engine was scrapped and a whole new one was built. This would give the game a new lease of life and would make it seem fresh and renewed before you even touched the controller.
Focus on a Single Character
Now that Treyarch have introduced the idea of an awesome story into the series the game's narrative has a chance to get deep and the easiest way to do this is to focus on a single character. More focus would let a player become really strongly connected to the character and this can only be a good thing.
What do you think the Call of Duty series needs?