Amazing game!! I think the first room of 1-1 being FUN even when I had to backtrack for getting all 15 stars is a sign of how good this game is. I didn't mind backtracking to get the 15 stars because it's just a joy to play. Kind of like how we've all probably played NES Mario Bros 1-1 a billion times, but it never gets old. Your stage design was really cool! I liked how a few of the stars eluded me at first until I learned how to reach them later on through experimentation. I also liked how you could bypass stars and had freedom to explore a bit before you had to focus on the objectives.
The movement and the hidden advanced mechanics (like the powerup star) felt so satisfying to use. Only suggestion I'd have is to make the groundpound Down+Jump or Down+Shoot instead of just Down. I played on an old controller with a sort of wobbly D-Pad so I had quite a few accidental ground pound inputs from that control scheme.
Really fun experience start to finish. Love the graphics, audio, and boss fight design! Incredibly authentic to NES style. Great work!!