Very cool game, definitely one of my favorites (despite not getting very far yet)! I didn't see anyone else mention this, but going back up the drill elevator (the first one, if there's more than one) softlocks the game since it gets stuck in the going up animation after one screen.
I saw other people mention giving the bosses' attacks more telegraphing. For the first boss, I notice it does have a subtle one, its eyes opening. Maybe this could be made a little more obvious by having them open a little further than usual, to distinguish it from the normal blinking animation.
Edit: I see the second boss (and only other boss, assuming I didn't miss anything) telegraphs its laser attack by closing its eyes. Maybe its eyes could fill with red to show it charging its laser? Or just around the edges of its eyes, to make it a tad subtler. Just a thought.
I look forward to seeing where this goes!