Bug: Picked up an upgrade which caused the ball to go out off camera, shooting again made it fly over the scene ignoring all collisions.
Playing on phone I didn't manage to hit a single ball in on my first try, maybe an indicator showing where the balls go, or increasing the size of the score holes would be a good solution to making it easier.
I think it would be a great addition to stop monster timers by 1 when scoring, it feels wrong to get punished when you did something right. You could add enemies which have their timer keep going regardless of you scoring later into the game.
I really like the idea of having buildings on the board which you should avoid hitting. It spices up the core gameplay, what I thought would be cool would be if you can have the ability to spend a resource (maybe gold) to place down new building where you want (windmills and houses for more gold, archer towers and guardhouses, A castle which resists a few bounces and adds an extra life but removes that life when destroyed, Walls which you can build around your buildings to protect them).
Either way cool game, love the art style!