You haven't played an MMORPG until you've played World of Warcraft.
It's incredibly immersive and overall the best online game I have ever played.
Good: Huge, beautiful, seamless world (as said in Gamespot's review); really good soundtrack; double experience system; addictive combat; incredibly intuitive interface; very time-consuming
Bad: Very time-consuming
If you are going to buy an online game, it should be World of Warcraft. It is definitely worth the monthly fee.
Also go and check out the expansion, The Burning Crusade. My character is a Draenei Shaman and I've having a really fun time whenever I play this game. It really feels like I'm in this whole other world.