Kingdom Rush is a tower defense game.  It is a casual game for an app on a smart phone.  You strategically put towers along a defined path to kill enemies.  After winning all the rounds in a section, you get stars to improve you defenses fom the start of the game.  You upgrade the towers to kill big hordes of the enemies and take down the bigger and badder foes.  It reminds me of Civilizaion and Actraiser in the fact that you control many players that help defeat enemies. You also grow you defenses during each section.

I love TD games! I have a very strategic mind to expertly place the towers in such a way that I get three stars in almost every section.  It is aesthetically pleasing so I don't mind playing it for a long time.  It really hard to find a good TD game, but I think Kingdom Rush has the right formula.  The only thing I wish they had was a fast forward button to kill the slow strong enemies faster.