Like any great expansion pack, The Burning Crusade doesn't just offer more of the same, and it doesn't cater exclusively to experienced players. It offers a lot more of the same, and it also adds a number of new features that can be enjoyed by newcomers and level 60 veterans alike. Perhaps the most significant additions introduced in The Burning Crusade are the blood elves and the draenei--two new playable races that have made the paladin class available to the Horde faction and the shaman class available to the Alliance faction for the first time. Both of these races have quite fascinating backstories that are revealed both through their respective intro movies and via in-game quests and conversations with non-player characters. Like the eight previously existing playable races in Azeroth, the blood elves and the draenei begin their adventures in specially designed starter areas where you can play without having to worry about bothersome high-level opposing players for the first 15 to 20 levels of your character's existence. Thereafter, the new races join the rest on one of Azeroth's two continents, where there are more than enough quest-filled environments and dungeons to keep you busy to level 60 and beyond.
It's only possible to advance beyond the original game's level 60 cap if you own The Burning Crusade, which unlocks new player skills and talents for characters through to level 70. It's conceivable that you could advance through many of the levels post-60 without ever visiting the new Outland realm, but it'd be a far more time-consuming and less profitable process because quests in Outland offer significantly more experience points and gold. Furthermore, Outland is the only place where you can advance your chosen professions beyond the previous skill cap of 300 to gather all-new resources and craft powerful new items. All of the existing professions such as leatherworking, alchemy, cooking, and enchanting can now be pursued to a maximum skill level of 375, which is also true of the new jewelcrafting profession.
source : Gamespot