Still the best multiplayer game online. Blizzard set a benchmark that others such as AOE, WAR still can't better.
You can take a character from 0 - 80 (60 maximum in the 1st version) in about 3 months playing about 12 hours a week. Others can power level far quicker but I'm guessing i'm a standard WOW player with no exceptional talents.
The different races and profession keep the game repeatable, so once you've max'd with one char you're likey to go back and start a new. Alternatively you can complete the mass of PVE dungeons or PVP arena's to get the best items and continue tweaking your char until the next game release, then start over again.
On the down side the Guild play is limited and Blizzard have not spend time in building a Guild vs Guild feel. This means that for most gamers they tend to drift between Guild's and unless active friends are in the same Guild there is little bind to stay in one for any period of time.
Finally, it is a time killer, great fun but make sure you have a comfortable chair... You will be spending a lot of time using it.