In Halo Reach there are unlockables that are bought through credits which mean nothing.
In Halo 4, I’d like to see armor that is unlocked by achieving 50s in certain playlists. For example, there could be a special chest-plate for a Team Slayer 50, a special helmet for a MLG 50, etc.
I’d also love to see really cool helmets that are unlocked by achieving a 50 in 5+ playlists, 10+ playlists, etc.
This would provide incentive and rewards for people who are good at the game. It will make them want to play even more because these unlockables would truly MEAN something.