Great job on building this game by yourself!! I really struggled finishing level 1 and decided to hop over to levels 2 and 3, beat them both a good 20 times and over time became super-powered. That was a great feeling, I didn't even care about taking damage, just scaling the mountain for that extra power-up. At the end, I could almost 1-shot everything which felt really great. I enjoyed the diversity of enemies, and had fun placing myself below the jumping boss while shooting at his "legs". Pretty cool and diverse set of music and graphics per world which made the game feel non redundant. Overall that was quite a fun game to play! I don't think there is an end?
The only quirk I would enhance is that sometimes it was hard for me to know where my character was relative to the platforms on the ground, and I would end up missing a platform on the way down from a jump.
Awesome job overall!