I really liked the art style in this game. Clean, simple, and stylish. The parallax background looked nice and the effect when the blue guys die was cool too. It could have used some sound effects for walking, jumping, shooting, and enemy death. Some background music would have been nice too.
When I jumped in one of the pits the player doesn't die, you keep moving left/right off screen. Having the player respawn at the beginning of the level would have fixed that. When I was directly behind the box in the beginning of the level the projectile goes through and over the box, which felt a little buggy.
It would be cool to see this game develop into something more after the jam!