This game has so much potential! It is a lot of fun to cause the fission. The feel of shooting is great The issue in terms of making it more puzzly is that you can kinda just shoot a ton of fissions and hide out in the doorway and they will eventually hit. It's kinda fun that that is a viable solution but I would like to see a level where you have to be a bit more clever.
The sfx are really great in most areas except the footsteps and the ambient light flicker. The light flicker becomes better in the last level when they harmonize a bit. Are the footsteps tied to the player animation? It sounds like they might not be.
You say you have music samples in the game? I didn't hear any music. I think you could have such cool music for this game.
Overall definitely one of the best concepts from the jam, so much potential.