I loved the art, music, and sfx. Reminded me of the SNES.
I also enjoyed the gameplay for a little while before it started to feel repetitive. I think the main issue with the gameplay is the level design. There are too many long sections of walking in a straight line which are usually broken up by narrow passages that only serve to make it impossible to jump over enemy projectiles. Also in one of the levels there was a section with enemies on the left (after a climbing section) which led me to believe that was where I had to go and I ended up just wasting time.
I think good level design for the current gameplay would involve more verticallity. This would make shooting more engaging as you would actually have to aim your shots at distant enemies.
The gun variety was awesome and I enjoyed experimenting with the different guns. The one issue I found with teh gun system is that the gun icons on the boxes are too similar which made it difficult to tell what gun I was picking up. The boxes also felt like they were randomly placed which was inconvenient at times where I needed a new gun or was trying to save my current one.
It would probably be clearer if the icons represented the bullets instead of the shape of the gun.
Overall this is a great jam entry and a few tweaks away from a legit game. Great job!