If you're on Facebook, you must have noticed invitations from friends to join them in an online game. A few weeks ago I decided to take part in a few games, what use is a game if you don't play it?
So I became a member of a mafia family in the Mafia Wars game. Later I got involved in Spymaster and lately I have been running a farm in Farm World.
What they have in common is how a player can grow from easy challenges to harder challenges, that get unlocked once a level is mastered. A level is mastered after a numer of experience points is reached. The first levels are reached quite fast. You win points, buy stuff and play with or against other players, who you may not even know.
These games run on top of Facebook, so they use the facebook knowledge of your friends network. And one problem may be that in order to play harder levels, you will accept invitations from other players, that you don't know. They will join your facebook network too. Be ware of this risk!
I will post a few game reviews in the next few days.