could be something similar as RoF, that you get gifts and medals for online achivements

Yes, I also like a system where you are rewarded as long as you manage to stay alive.

Very nice idea :)

Not just yet though, MP crashes every single time I play after a random amount of time :P

On a serious note: Stats are something that keep players coming back for more. Look at the retention the Call of Duty series has; As a social COD-player myself, I can tell you it's not for the gameplay, but the unlocks and stats - keeps it interesting!