I think you should change the colors for the platforms that you can jump on and the spikes. In my head, the spikes were lethal and the platforms were not jumpable because the structure blended with the background. You can easily fix this with a color swap.
You did a good job with the tutorial stage but failed to teach the player that they could hover and they can shoot while hovering. When I got to the boss fight with the vampire, this was essential to know. I think the boss had way too much HP; especially for the first boss in the game. I also thought that the game was way too easy. It gives you so many health upgrades and hearts laying around that I actually brute forced my way to the boss.
This was a great looking game and I enjoyed playing it. Keep it up!