I don't what those green/grey things that came from the top of the screen were, but the background looked great.
The bat was a bit floaty which I personally found not so fun, and the tiny hitboxes and only being able to shoot horizontally made hitting things difficult in an unfun way.
I don't know if it was a bug or by design but the audio was also kind of noisy/glitchy at times which was really hard on the ears.