Samurai vs Zombies Defense is a wickedly entertaining panning defense game where you play a samurai attempting to defend your shrine from zombies emerging from a portal to hell. Along the way you'll unlock new allies, abilities, enemies, and ways to lose.
I was originally trying this out on my HTC EVO thinking it was a tower defense game (which are sort of my thing). But it's not, and the gameplay isn't something that initially appealed to my tower defense-loving self; however, in terms of sheer captivation, this game managed to consume about 80 percent of my 4000mAh extended battery today.
Samurai vs Zombies Defense is free, although it's on the GLU network, which means there are options to upgrade things sooner for cash, or downloading other games, or perhaps hiring yourself out as a real life hit-man (I'm not sure how far down the incentives go). The game appears completely playable without the easy money for real money, though some people are complaining that level 33 is unbeatable without a purchase. After a day of playing, I'm at level 12. Your mileage may vary.
Download: Google Play