The pixel art and animations are top notch, the music is superb, the player attacks are satisfyingly snappy, the enemy AI has variety, the plot feels like it's ripped straight from an old school NES game, and the core mechanic receives full marks for creativity and fitting the theme. The fact that this was made in 48 hours is nothing short of outstanding.
I have very few critiques. The main character feels a little slow since I prefer faster-paced games with quicker player movement and enemies, but that comes down to personal preference. I also experienced a bug where one of the enemies walked off screen and couldn't be attacked until he walked back (although he could still shoot projectiles at me from off screen). Outside of that, I just wish there was more content. More enemies, and maybe some varied level design. Nothing that isn't immediately excused by the time constraints of the jam.
Full marks all around. Well done.