I played this game on hard, I beat the two levels mostly avoiding the enemies. You put some snails when I have to make jumps to the other platform, I let myself get hit by the snail and while invulnerable I made the jump. Those snails are really a pain with their health and vulnerability window .
The art style is cute, the combat is hard against the enemies in general because it stop the player's movement, also I feel like enemies have too much life, it will be more fun is they need only one or two hits to be defeated. The double tap for running is very strict, maybe make it more easy by increasing it.
I would say it have that retro difficulty from the Nes era for sure, but combat is not rewarding, I mean, attacking enemies will mostly get you hit because they have to much life and you can't move. Lowering the health will make it a reasonable strategy try to attack enemies instead of just avoiding them and running away from them.
Keep up the good work.