I got sucked into WoW for awhile. I don't play anymore but it can definitely consume alot of your time without you realizing. You can make friends on the game. You can explore. You can do Player v/s Player (pvp) and player v/s environment (pve). There are achievements you can get, and you can collect ground and flying mounts. Leveling up a character for the first time can be very fun. Once you reach level 80, getting better gear becomes the main thing. But eventually you get to a point to where you've done everything the game has to offer and that's when it got boring for me.

Everyone is different but I found PvP to be the most fun, but eventually I got too overpowering to the point that I hardly ever died. That might sound like a good thing but it can be quite boring when fighting is no longer a challenge.

And like Gect said, Horde Rules.