I had to play the game twice to eventually understand that you need to jump under a platform then jump again to reach it, that's unintuitive (and that the left and right edges of a platform are solid doesn't help), and I guess that in the end it almost felt like finding a secret so it was fun by itself. ;)
Once I understood this (I wanted this shotgun! and it was worth it) I enjoyed my short time playing the game, with the right difficulty and a fun boss fight at the end. Very fun game, thanks for sharing!