It’s a never ending alternate reality. Not only for yourself but to those who share that environment (guilds, raid teams, instance groups, etc.). As WoW is one of the largest MMORPG's in the world, one feels a part of something different (especially if your character is pimped out and others are telling you so… it’s a good feeling).
But on a serious note, the addictive behavior is not to be taken lightly as it can affect a person in various aspects, environmentally – alienating oneself from family and friends or poor performance at work for example – as well as physically do to lack of physical exercise (of course it may vary depending on the hours of play). It has also been shown that obsessive behavior may lead to anxiety.
Following the scholarly article, Harmonious Passion and Obsessive Passion in Playing Online Games and other research what some avid WoW players experience is simply a harmonious passion for the game to be described as something one enjoys or finds interesting which leads one to devote time and vigor to the game.
And on the negative note, obsessive passion is similar it’s the control factor that make the difference. From what I have studied and read, people with obsessive tendencies tend to latch on to particular things. Wow is one of those “things” that can lend itself unintentionally as a means to addiction. In my personal opinion the game itself cannot be made culpable of such behavior. Lack of control is primarily in the individual and she or he should seek help depending on the severity.
All in all I am a huge fan of WoW, and confess to be harmoniously passionate about the game. It’s great entertainment and an innovative bridge to global socializing.