Awesome concept and good execution. The art and the music are pretty great. The controls are simple and work fairly well. You've also done some pretty cool stuff with the level design.
I did have a handful of issues. On level 3, it's possible to shoot yourself into a corner and be totally stuck. I don't know if there was a reset button, but I wasn't aware of it and had to reset and replay from the start. For a game like this that has no movement mechanic other than static objects in the map, you really need either a level reset button or to be extra diligent in placement of everything.
As far as the difficulty, which I know has been mentioned a lot, I think there are some ways to mitigate it a bit that don't necessarily need a lot of extra levels inbetween to build up skills. I only got to level 4 because I suck. I felt the main thing that hindered me from doing well on that level was the extremely restrictive FOV. The first thing that struck me (literally) about the level was that there were spikes that I had no way of knowing existed and no way to slow down in time once I saw them.
I died to those spikes a lot even once I knew they were there, and I think the biggest reason was because I couldn't see them to judge the distance against my momentum. Eventually after a bunch of deaths, I had the right momentum down, but that feels a little like artificial difficulty. I had the same issues coming down the other side, not because I didn't understand the mechanics or how to use them, but just because I couldn't see things to judge distances.
Your game already has the ability to be challenging on the strength of its mechanics (as I'm sure the later levels I didn't get to show), so I don't really think it needs artificial difficulty in the form of restricting the information available to the player. It already needs a careful application of speed and good reflexes just on its core design. I think a suitably wide FOV or even a stationary camera showing the entire level would benefit it greatly.
Sorry for the novel. I really enjoyed the game, and the camera started hindering that enjoyment after a point so I wrote a lot of words.