Best Multi-Player Game in the AppStore?

What do you think the best Multi-Player Game is the AppStore? I've been looking for some new games to start playing and was hoping somebody has a good one I haven't heard of. I have typically enjoyed playing games like Metalstorm that are First Person, but games like Fruit Ninja and Tiny Wings have a special place in my heart as well.  What makes a game good on iOS, what makes a game suck? Just a few fruits for thought.