Besides account level, we should have seperate levels for our classes and have a progression teee that unlock additional stat bonuses, weapons, abilities and perks exclusive to that class. Perhaps get skill 1 point every level that we can use to unlock a path of our choosing at the relevant level.
Examples could be,
Scout:
Recon Tree,
Lv 1 Unlock Predfalcon ability: The scout calls apon a trusted falcon who flys around the predator for 30 seconds and picks out targets.
Then further down the line near the end.
Lv50 Scout, Predfalcon is able to spot concealed targets.
For the Fireteam you could have;
Assault;
Explosives experts tree;
Lv 1 Unlocks grenade underbarrel for assault rifles, has a separate ammo count from frag grenades.
Lv 50 Assault, underbarrel can now rapid fire impact cluster grenades.
Adding character progression will keep players grinding away at exp to build their own optimal characters and allow for a wide varity of builds and tactics. That will in turn increase replayability as gameplay in matches will vary and keep people on their toes.