Hi there, the art style for the game really nice. It suits the calm manner of the game. The game play is simplistic to learn and would be a great idea for a tablet based casual game. To improve, I would recommend using a Coroutine to act as a counting system, tracking the amount of time the player has been and using said variable to increase the spawn rate of the enemies. This would improve the challenge scaling and create more replay-ability as the challenge would create a sense of competition, along with the high-score system already included.