It's a game.
The most addictive game I find is fruit ninja and angry birds on the iPod Touch.
I played WoW for 3 years, the community got terrible, game content got worse, the game is getting old. Newer MMO's are attracting more of the players because of what they have to offer.
There's no possible way you can argue against the fact that it has the highest subscription number ever, sitting at 12 million subscribers as of October, until The Old Republic comes out. Cataclysm is attracting old/retired players as well as new users to try it out, like me. Make that 12,000,001.
[Edited by yosup, 11/25/2010 2:19:10 AM]
He's actually correct. The title says most addictive, the first post asks about the "Best" and the poll contains the latest releases.
Most addictive, best and newest do not all go hand in hand. Addictive defines what you can't put down, but defines no level of enjoyment. Best defines enjoyment not age. Newest only tells that it's recent, but it could really be a steaming pile of cow dung.
In short: The topic creator didn't think this through.
To answer the original question, right now I find Assassins Creed the most addictive, and I refer to the original. I find that whatever is most addictive changes since playing a game too much makes it stale. About the most addictive game I ever played was Final Fantasy X.