Modern Warfare developer Infinity Ward wants to give players the ability to customise their respective soldiers. Call of Duty players will be able to customise the appearance and weapons, with the ability to unlock new operators and camouflages for their weapons.
When playing multiplayer, players can select from two factions: Allegiance and Coalition. At level one, there will be generic character models to choose from but as players progress through the game, new soldiers with somewhat different personalities. No character offers a gameplay advantage, they just look different!
Although it isn't possible to fully customise you soldier of choice, there are several operators to choose from and there will be plenty of new operators that are going to be introduced post-release. Each operator will have a certain number of skins according to Studio Art Director, Joel Emslie.
Infinity Ward wants players to spend more time modifying their weapons in the Gunsmith, rather than tweaking every possible item of clothing on their soldiers. The goal is to make a lot of unique attachment combinations for every weapon in the game in order to get the upper hand against the opposition.
Infinity Ward aren't too worried about players finding a combination of attachments that is deemed to be "overpowered" as there will always be a counter for them.
In conclusion, spend plenty of time creating the ultimate combination of attachments for your weaponry rather than worrying about what your character looks like on the virtual battlefield!