The Burning Crusade is an excellent expansion to an excellent game, but unless you are high-level, hold off on buying it
Graphics: Obviously, World of Warcraft isn't a shining beacon of graphical acheivement, at least in a technical sense. The lighting isn't great, the models aren't bursting with polygons, and the textures aren't hyper realistic. However, The Burning Crusade has a magnificent art direction that makes the game beautiful despite the fact that it isn't the most graphically advanced out there. The zones of Outland pack an artistic, visual punch, from the haunting-but-lovely Zangarmarsh to the pastoral zone of Nagrand. Upon emerging on the other side of the Dark Portal for the first time, I was stunned by the wonderful look of the sky above Hellfire Peninsula with its moons and the streaming green aurora above. The Burning Crusade looks very, very good.
Sound: The music of the game really helps set the mood for the zones you are exploring in, and thankfully, it wasn't all lifted from what was already in the game! While the soundtrack isn't fantastic, and that peaceful tune in Zangarmarsh doesn't really fit when you are being shanked by a lost one assassin, it is consistantly good throughout the entire game.
Value: The new zones in Outland are filled with quests and new things to do... if you are level 58 or above. In all honesty, if you are not high-level enough to go through the Dark Portal, you can hold off on buying this game unless you absolutely must play a Blood Elf or Draenai character, or if you really, really want to take up the new jewelcrafting profession. Otherwise, if you are ready for what Outland has to offer, The Burning Crusade makes for a great addition to the World of Warcraft experience.
Tilt: The Burning Crusade is a genuinely enjoyable experience, and remains so even after wading knee-deep into it. Even after 70 levels, it continues to be fun and enjoyable, and it provides an incentive to play that most other games lack. If you are high-enough level to experience it, get this game. If you aren't, at least you have something to look forward to once you are.