4. Angry Birds
You can trace the roots of this Apple App-Store bestseller back to other artillery games like Scorched Earth, but the genius of this game's developer was replacing tanks and guns with cartoon pigs and birds. To wit: Pigs have stolen the birds' eggs. The birds, now righteously enraged, place themselves in slingshots, and — with your help, of course — fling themselves into poorly constructed buildings, forts, etc., and try to off the pigs. The combination of simple mechanics, compelling graphics (like the way the pigs snort at you if you fail a level) and the stars-per-level system, whereby replayability was increased tenfold, made this a global phenomenon.