A solid entry for the jam. Have no complaints apart from some nitpicks which do not affect the overall experience of the game. One of them is having a mini-map would have helped a bit and the other is that enemies could be hurt from a distance that made it a bit easy for me as I could kill some enemies from afar. Sound FX bugged during my gameplay maybe a small issue but it felt like sounds were all over the place.
Now the best parts of the game, first and foremost the game design. I loved your approach of having difficulty variations in different areas. Best one being enemies guarding 3 coins. The health pickup on power up was a clever trick. It forced me to pickup other weapons even if I had the best weapon. Kept the difficulty at a level which wasn't too difficult to be frustrating or too easy to be boring. Graphics were really good and were looking pretty. The boss whooped my a#s for the first playthrough, will come back to beat him later. Overall a great entry and I can see you getting good rating from so many people.