Clever idea for a game! Even though it's a very different style, it still has the classic metroidvania sense of progression. It was very satisfying going back through the early bits that gave me trouble, now with several extra strokes that let me fly over everything.
There were some issues things being off screen though. In some areas the camera is locked and you need to shoot the ball past the edge of the camera to move it. In the later parts of the game there's also the issue of being able travel so far it's hard to tell where you can go. It took me a while to find the final stroke upgrade because of this. Perhaps some way to zoom the camera out could have helped.