Thanks for the feedback!
I'll clarify here about the plans. Initially, I planned the game with the mechanics of shooting diagonally (like in Dangerous Dave 2), correspondingly balanced enemies. From the interactions, I planned for the game to have buttons (levers) that open doors or launch platforms. Yes, doors. Like in the same Dangerous Dave - transition to different rooms on the level. Rescuing hostages (not required for passing). And also the main mechanics: breaking boxes (either with a shot from a gun or with a downward blow in a jump), collecting coins (I haven't figured out what for, increasing experience?), finding keys and secrets.
There was still enough memory in the ROM for content for a demo of one level (presumably). But, most likely, I lost interest. When I get to the stage when I need to make content - for me it's stress :) I thought it would be easier to make content for a 16-bit system, but no (there are nuances here). Although I have done enough in the logic of the game that it would be a shame to "throw it away".