OK wow, I am completely addicted to a new Nintendo Wii game that I got for Christmas. I had this same game back on the Gamecube and got totally addicted to it as well. But since the Wii has the ability to connect to the intranet the addictiveness is mucho grande!
What game could it be you might be asking.....

Its a simple enough game, you have a character that moves into a town full of upright walking and talking animals. You do basic stuff like fish, dig for fossils, buy furniture for you house etc... Yet even though it is a simple game, it is crazily addictive. Then add the ability to visit other gamers towns via wifi and this game steps up to a whole new level of addiction! Now not only can you buy and sell and fish and dig at your own town... but at other peoples too! YAY!
Ah, just sitting here writing this makes me wish I was at home with Wii Remote and Nun-chuck in hand..... Oh, and its totally one of those games that makes no sense to people who havent played it, but trust me, its good mind numbing fun....