While the post on the Call of Duty community page doesn't delve in to much beyond the class details, it does go in to what perks each class will receive.
The first of the four classes, the Weapon Specialist, receives a 20% bonus to weapon damage and better weapon handling through level progression, while the Medic revives allies quicker and receives a speed boost as well as healing abilities as the character levels up.
The Engineer seems to be a vital addition to any squad, providing armor for the drill used to penetrate the alien hive, and extra cash. Drill maintenance and trap efficiency also improves as the Engineer continues to level up.
Last but not least, the Tank is just as it sounds, granting the class 25% more health, the Tank also benefits from even more health powerups as they progress.
The post mentions that the most successful teams will consist of a variety of these classes, with players using the abilities and classes to compliment each other and eliminate the alien threat.
Call of Duty Ghosts will release for Xbox 360, PlayStation 3, and PC on November 5. It will also be released at launch for next gen consoles.