Cool game! I enjoyed the music and the slow motion fit really well with the game. I thought it was interesting that I could kill myself with the gun, surprised it wasn't a secret ending. I also never got to any stages beyond the first, although I see a few others in the screenshots, am I missing something?
If you wanted to improve, I suggest an 'arcade' mode where there are several other enemies and that each time the gun is used, another spawns. You could even take that a step further and experiment with it as a local or online party game. I think it could have some real potential if mixed with a bunch of other western style minigames.
Overall, super fun!