I reached wave 10, i think it only plays with the mouse so it would be cool if it tells you that somewhere, i think the collision of the snowball should be a little larger since i had moments where i trought that it would surely hit but it didn't. The upgrade system is good but i think you should start with a wall at the beggining of the game because is fundamental since you don't have any other way of evading the snowballs when they throw them at you and it could be frustranting watching it happen and don't be able to do anything to prevent this.