Fun little game! I agree that the player trail is great, and I like the lighting and overall aesthetic. Would be nice to have some sound though!
For the controls, I think the speed and jump height of the player were well-tuned relative to the environment and enemies. One issue I had was I thought the camera was a bit too high, and would also follow the player up when jumping, so I would often be falling blindly and then hit spikes or an enemy that I couldn't see below me.
The shooting was satisfying. I kind of like the spam-click style, but I could see people wanting some auto fire when holding the button down. It was a little awkward that the projectile firing point was so far from the center of the character, so if you shot straight down when standing on one of the moving platforms, you would miss the platform. You could still hit it by standing on one side and shooting the other side though.
Not having checkpoints or healing was a little frustrating, but when you respawn you keep your crystals and they also respawn, so I was able to get to the end comfortably still. Overall well done!