In a deviation from the time-tested multiplayer form, Activision announced that the newest iteration of the Modern Warfare franchise will feature classes which will separate playing styles. The classes are:
Assault: Gets standard set of killstreaks
Support: Unlocks the lesser offensive skills (UAV's, Turrets) - Doesn't have killstreak reset on death
Specialist: Doesn't earn a killstreak, but will unlock perks after every second consecutive kill
You can extend streaks by capturing objectives and providing assists to other players. View the video below for all the details:
Source: CallOfDuty.com
looks amazing :D