The shooting mechanics worked well, and I liked the use of the particle system and the different angle for the lighting to give it a "doom" sort of darker feel. The challenge was maybe not super high as I had to intentionally get hit to test whether I could take damage or not, but that just means you have room to scale up the challenge with future levels etc. It's a good idea for the initial experience to not be overwhelming. I liked that you had some variety to the enemy designs.