if you are planning to update this at any point, maybe roguelike/roguelite mechanics? As far as i can tell this doesn't have any. Also maybe tune monstro down a bit.
And maybe replace the health, boss health, and bomb sprites with your own versions so they at least aren't directly ripped from the game.
Don't get me wrong, cool project, i think it's mostly faithful to the original game, but imo with this you should either try to diverge from the original, or re-create it as closely as possible (but then you'd have to make it free so it's not seen as scummy, i guess)