I think it would be better if the game started in a room where you could get used to movement and shooting, (which can only shoot 4 directions due to GB Limitations), before going straight into the action. There's also no indication of what the upgrades do unless you try them out yourself (I understood the health upgrade, though). Once you do get used to the controls and slow shooting, though, it becomes a tense and fun game containing enemies with unique traits you can learn (even if they become repetitive after a while).
The use of Midas really fits the theme of gold. I liked the abstract art direction and the music is atmospheric despite not sounding like it came from a Game Boy (though I found it abruptly cutting to the beginning quite distracting at points).
Overall, I can really see this working well as a Game Boy interpretation of Binding of Isaac's gameplay despite its issues.