A great game, but don't get addicted!
World of Warcraft is probably one of the most addicting MMO's I have ever played. While you are leveling, you're always waiting to get to the next level to get that talent point, equip that new gear, or get those new skills. When you're at max level, you're always after new gear, raiding spots and PVP. This game can keep you busy, no doubt.
The latest expansion packs have made everything before it useless, so once you hit 60, buy BC, do a couple quests, you have better gear then you could get in Molten Core.
Although this game has gotten a lot of attention, and Blizzard is a well respected company (who is making A LOT of money now...) I would recommend you monitor your time on this game. It isn't worth sitting on forever, because this is one long-ass time consuming game.