Zynga's Mafia Wars is anything but low-bar. It might not be much to look at, but their execution has been nothing short of brilliant to this point. They flat out COPIED a game that was huge on Facebook (Mob Wars) and iterated their way past it. They relentlessly used short iterations, A/B testing and customer validation to beat the established competition.

Mafia Wars is now 5x bigger than Mob Wars.