Nice and simple game. I think it takes a bit too long to "destroy a dream" aka vanquish foe, so eventually they will get through. Could decrease enemy speed, health, or increase water/bullet damage would help. Can't tell how much HP the Castle Wall has, adding some sort of indicator would help a lot, either a number, visual damage, or changing color. I'd love to see some powerups to mix-up the  gameplay or maybe skills that cost dreams. Then you could add spray nozzle, repair walls, super water/bullets, slow down, poison, etc.