Thanks, all valid feedback.
For the artwork, I drew them in Aseprite. I used a single colour palette to try to make it cohesive. Definitely a bit of a time sink.
Not to make excuses, most of the code was done in the first 2 days when I had time off. The rest was built around my work schedule. I had to pick my battles. For example, the button placement was originally a control panel. But I felt converting to mouse input and contextual buttons was more user-friendly. 