An overrated continuation of the original World of Warcraft concept.
The original World of Warcraft had it's charm, but it was just a great failure at some points.
The original Warcraft story was blatantly raped continued by another team of developers who had apparently not read any of the original Warcraft lore. The leveling system was boring and it became repetitive after the first thirty levels. The end game raiding of the game also required you to spend plenty of time online in order to aqquire some of the best gear.
This concept was apparently very appealing to some gamers, but others just got bored and went back to the games that they used to play after a while.
The expansion to the original World of Warcraft, named the Burning Crusade, didn't bring much originality to the serie. What it brought was more raping of the story, more mindless grinding and raids that required even more of your time in order to be a successful. It's basically the same thing as the old game, with some minor new features. Although I'll have to admit that there are much worse games around, and the Burning Crusade will be fun for some hours, just like it's older brother.
So, basically, if you enjoyed the previous game and want to continue in the same track then I recommend that you buy this game. However, if you don't want to spend money on the same thing then I suggest that you look out for some of the new, upcoming MMORPG's.