Ninjatown

Not as safe a place as you might think.

"Borrowing an existing game design can work if you inject it with your own personality, and that's exactly what Ninjatown has done. Tower Defense is already a fun game, and most things in life can be improved by adding ninjas. The brief devil invasions here (around 10 minutes each) are perfect for portable gaming. Add in the friendly single- and multicart multiplayer modes and Ninjatown offers a pretty high quality of life."