I liked your minimalist shooter but the terrain is unforgiving, and the enemies are too fast. So I recommend that you fix one of the two: 1) reduce the enemy speed so that the even though the terrain is irregular the player won't feel like it's too hard from the get go. (2) Or make the ground a flat plain at in the beginning few areas so that players don't feel dejected.
Also you'd so kind and rate my game I'll be grateful!