A few things I think you could do to improve the game.
- Reduce the damage from enemy shotguns (They can be very frustrating, especially when you increase the difficulty. It could just be me)
- On the first level, I think you should expand the yellow rectangle where you "slide jump" off all the way to the edge in the front of the block (When I first started playing, I thought you were supposed to jump right on the rectangle. It took me a while to realize you were supposed to jump off the edge)
- A boss could be pretty cool, but i'm not sure how you could implement it into the game. It might ruin the fast pace of the game as a whole.
Overall, one of my favorite games. It's very fast paced and the graphics are amazing. Also, are you gonna add a price to the game on steam once it's completed? If so, how much will it be?