Great game you are building, keep it up!
Here are some of my thoughts:
• It was good to have remapable controls, but I couldn't use K to jump as it kills the char, I had to remap to WASD keyboard + mouse, but it turns out I can't use A ans S as they are used for weapon swapping, so I had to give it up and plug in my gamepad.
• Graphic are cool and stylish.
• Sounds and music are joyful.
• Checkpoints would be helpful (at least for first levels, or for normal diff if you'll have diff levels).
• Game is very hard, but it was that fun that I gave it more tries than I would usually do, lol.