Yeah, This game was really difficult for me as well despite having played games like it(Starsector). balancing, pacing, etc... So much to do yet so little time :(
I just reached the shop and found another bug. Before the shop appears there is a ~1s window for the player to take another shot. If the player begins taking aim and the shop appears, then after the shop is closed the ball is automatically shot. If you buy an item then the ball is shot not where you were aiming previously but in the direction of the purchased item.
Have you thought about using different shapes for enemies. Maybe a boss that is a square, minions that are triangles. Maybe even an enemy that's too big to be scored and you need to do something to score it(a giant circle with a small weak spot which when hit reduces size, it could be a boss fight where you need to hit that weak spot multiple times).
Here's another idea, Maybe you can also have shields enemies with tiny shields which face you when your ball is still. Forcing you to make a bounce shot.
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).
