I really liked exploring in this game. I got big metroidvania vibes which I like a lot. I have to agree with Hazarth that the shotgun jump feels better than just pointing down. Having that function on it's own key made the controls feel tighter. I had to play on Easy before I realized how to reload. I would have loved to be able to reload with R or have it be automatic when hitting 0 shots left.
Having extra shells as a collectible is a fantastic and simple idea that gives the player more exploration options without having to add different mechanics or power ups.