Need to say, doing a game for NES was unexpected, and it's certainly an impressive feat for me, so nice job!
Altought sincerely, the game itself is way too simple as is, and since it has only 2 screens it barely feels like a Metroidvania (It feels very incomplete overall tbh). I was also pretty sad you couldn't stomp the enemies, specially since you used the Mario sound effect for jumping x3
The art is also kinda messy, basically every platform gets mixed togheter with the background deco so it's hard to tell where you can step or not at first. I know NES has a limited pallete but even then that usually isn't an issue for real NES games.
And I guess that's it, there's not much else to comment about. I still appreciate the bravery of going for assembly, and the cover art is pretty awesome too