Wow, this game is amazing. The art and sound you chose were consistent with the game's style. The retro music is superb. The dialogue at the beginning was great.
The gameplay feels extremely satisfying, controls are responsive and quick, level design is great (except maybe for the boss level, needed a bit more time with that one). I love that you added a few secrets.
I only found one tiny bug where at the very beginning you can fall off the level to the left (I was looking for a secret :D). But other than that, knowing that this was your first ever 2D game and made in a 3-day game jam is insane.
Good luck in the jam, man!