Hi there
First : know that I didn't have a bad time playing and that's a nice try. 

Buuut... there are too many things going wrong ! I won't speak about technical problems, because you probably know them, and I'm sure you will improve.

In terms of design, I think you just tried to do too many mechanics and too many content ! 48h is a very short time, and you have to concentrate on the essential.
My advice would have been this : keep the HP shared with amo mechanic, get rid of : collectibles, platforming skills, crates,...  The question you should ask yourself is : "What is THE gameplay idea I want to do in my game ?" once you've answered that, cut the rest, it's just a waste of energy.
Speaking of which, you should spend more energy on doing feedbacks ! We HAVE to know when the enemy is hit, when we are wounded, when a shot is doing something or not (I tryied to break a crate with one shot : no sound, no animation, no new aspect = crate does nothing, it's just a part of the environment)...

Failures helps improve, in condition that you find what have failed.  So I hope this comment will help you, and if you keep on trying, I'm sure you'll make great games :)

Anyway, I hope you had a great time making the game, because in the end it's all that matters :)
Jams are made for this : try things and enjoy.