Battlefield: Bad Company had a cool system.
After you reached the highest rank in the game, every player you faced suddenly received a number. In this system, 50 was the lowest, and 1 was the highest. The thing is, though, only one or a few players could hold the number 1 at a time (I can’t remember how the system worked…). If you stop playing, you’re number goes down. Because there is no real “Slayer” equivalent in the Battlefield games, one has to gain points to maintain their “rank” (kills, assists, capturing/defending objectives, squad actions such as healing or repairing, etc.). If you’re at a 50/50 KD, you win 50% of your games, and you sometimes help with Objectives, you’ll likely sit around a 25 out of 50 or so.
If this idea was applied to an improved version of Reach’s Arena system (where you receive the 1300-1700 level score), I think this would work well. If you want a good rank, play well. If every action had a properly proportioned amount of points attached to it. For example, a flag carrier will get tonnes of points carrying a flag back. His allies will gain points for killing the enemy players attacking the flag carrier and will gain a small bonus if they capture the flag. In King of the Hill, killing players inside or outside of the hill will gain bonus points on top of killing a player, while teams in control of the hill gain a small amount of points (so teams aren’t obliged to dogpile into the small little Objective area). Certain actions will dock points (betrayals, suicides, idling, etc.).
As a reward, I guess you’ll just get a sweet symbol next to your tag the better you do. If you manage to get a 1, 2, or 3, maybe that can show on your Service Record or something. As long as doing better does not correlate to armour, Firefight voices, or any kind of customizable part of one’s character this system can work.
This is just a rough idea, so obviously it could use work. Still, I think this would work better than the Credit system where players grind Firefight for their shiny emblem.