There quite a few unlockables in Gears of War: Judgement on the Xbox 360, and just as much (or more) exclusive DLC content out there as well.
This list contains all of the unlockable multiplayer characters, weapon skins, characters, campaigns, and more.
Don't forget that if you really want an exclusive character or weapon skin, and you didn't pre-order the game, or if you pre-ordered it at a different store, you can always check out the Gears of War: Judgement DLC on Ebay. A lot of people sell their codes on Ebay, so it's an easy way to get the other exclusive promos.
Unlockable Multiplayer Characters
This is a list of the multiplayer characters that you can unlock in Gears of War: Judgement.
Baird (Aftermath) - Unlock any achievement
Cole (Aftermath) - Survive ten waves in Survival Mode
Loomis - Complete the primary campaign
Minh - Earn ten stars in Campaign Mode
Paduk (Aftermath) - Complete the Aftermath campaign
Tai - Earn 126 stars in Campaign Mode