We’re adding content to both existing continents as well as to the zones specific to The Burning Crusade. We’ll also be opening some dungeons in the old continents such as Karazhan in Azeroth and Caverns of Time in Kalimdor. Many new quests will be integrated to the existing cities that pertain to the expansion. Because this content is part of the expansion, players will need to purchase The Burning Crusade to engage in it.

He also gives some insight into the new Alliance race and the Horde Blood Elves as well as socketed items, jewelcrafting, flying mounts and new zones. You can read more at Gamespot.