Added the DOOM Marine Armor (Praetor Suit) as unlockable perk for achieving maximum multiplayer level cap (wccftech.com)
Extensive character development system: you learn a great deal of ways to victory as you discover various unlockable perks, items and fighting styles. (gonintendo.com)
The rewards are usually XP for more unlockable perks which comes in really handy. (cogconnected.com)