Cool game!
Wish it had more audio, but the general gameplay was enjoyable. Needed a bit more polish in some areas.
The climbing mechanic wasn't obvious at first, I made it past the first screen where you're supposed to use it by jumping at it enough and forcing the collision to work, but soon after the level design made it more clear what you were supposed to do. It was a bit unclear that you could jump off trees because you have to be standing still, but it was consistent once I figured that out.
There was a point in the caves with a block slightly higher right on the other side of a screen transition, which made it seem like the screen ended there. I'd try to keep block levels the same across area transitions to avoid confusion. Making a more distinct tile for the one-way collision blocks you can walk past vs the standard tiles would help in making the cave area more readable as well.
Overall though it was very nice! I enjoyed going out of my way to collect the extra treasures and explore the map, and those massive snakes made for a real intimidating foe, having you backtrack through dangerous areas at times to get enough hits in.
Graphics were very nice, though the water reflection took away from the NES feel, and clashed a bit with the artstyle outside of that. Maybe some sort of dithering could achieve a similar effect?
I do agree with others saying crouching and shooting could give you a different shot arc.
Great start though, hope you expand on it o/