MaxxieBytes

@cooljammer00: It basically unlocks an extra zone of the map which you can access at any time, but its suggested going at level 30. Also, The main quest will reference the DLC content if you finish it before finishing the main quest, while the dlc will mention stuff in the main quest if you finish that first (up to the final fight which ends the game and is where you'll reload once you finish, Like pre DLC Fallout3 was.)

I literally just finished the quest they are starting on. Lol.