The first thing that came to my mind was full-screen effects, such as vignette effects. For example, green for good moves and red for bad ones. Big combo text or multiplier text would also help keep the player in the loop, and you could add audio feedback to make it even clearer.
From your comment, I gather that you have experience with shaders, so maybe you could make the bullet leave a mark when it hits something. That way, the player could trace its path and plan for a better shot next time.
As for shaking the trees, maybe there is a way that doesn't require actually making shaders. You could use the tree's transform component, or even add a little cutscene where the camera moves to the tree view, shakes the camera/screen, then fades out and back in with the cat on the ground.
Those are just the things that crossed my mind.