This game is a re-birth of the old Casio Calculator game back in the 80s. The original spirit of the game is retained but with new features (a.k.a. weapons). You will still be tapping away to shoot the invaders, but at the same time, by completing specially introduced quests, you will get to use new weapons to help you clear the more challenging levels. It is simple game to start of with and fun for all ages.