Feels, looks, and sounds fantastic!
The only problem I had was chunks of walls that were still "collision active" but might look like debris. Learning that you really need to shoot the bottoms of the panes to avoid this in the first few levels took some trial and error, I wonder if some effect could better differentiate debris from "collision active" sections that are still attached, but I understand there is limited visual space to work with in black and white.
Overall I think its just a wonderful, atmospheric, addictive, minimalist art shooter (with upgrades, nice). Great job!