Good presentation and Visuals. Enemy types are varied enough to create different gameplay situations.
If you are having such a vertical level design, I would suggest you implement a vertical attack as well, or being able to slide in the walls so you can shoot enemies easier. It was hard in some vertical platforms to get rid of the flying robots.
What about rewarding the player with regaining health when killing some enemies? I found that you can run pass almost all the area without fightin except for a couple of cube enemies that were blocking your way, and it's really easy to get killed when a lot of bullets are coming in your direction
Other than that, I think it was good! :)