Nice first game! I like the mechanic that player can use the force of the gun to "double jump". I would recommend to polish the game a little bit tho. Here are couple of things I noticed:
-Enemies/player hitboxes are pretty big. Hard to dodge things.
-Camera is centered to player all the time and there was times that I did not know is that bottomless pit or should I go there.
-When player dies, there should be some kind of info what is going to happen next, will game start over or what.
-Controls were easy to adapt to.
I played to the level where player have to shoot water drop enemies to make water level rise (btw I liked the idea a lot!). Then I did not know where I should go, but I'll try it later to see if I can figure it out.
Overall nice game and with a small polishing it will be even nicer!