Wow, this game is incredible.
The art is very stylized and the sprites are great. There is enough variation in colouring of the sprites to make it not seem so repetitive (slightly different shades of green for trees, different green for the ground rectangles, the addition of tufts of grass to break it up, a few different kinds of fish and sharks). The fish movement is pretty good. The sharks get a bit jittery when you hover over top of them, but then they swim down lower to follow you instead of staying at the surface. The bosses all looked interesting (Davy Jones' locker lol). The explosion animation was nice. It did seem to go on a bit too long on some bosses (maybe it kept going if i kept shooting them). The clouds were a nice touch with the great use of parallax and transparency to give them more depth.
The combat minigame is interesting. It broke up the game so it didn't feel like you were just flying around shooting everything so much. The mix of fighting styles when fighting the bosses was cool (shoot the boss in the overworld, but then they throw other enemies at you and you have to do the combat minigame).
Being able to upgrade your damage so easily kinda trivialized the game. Once you got to about 100 damage, you could just one shot most of the sharks. I ended up taking more "damage" just from having my max hp raised.
The tutorial was quite helpful. I found out very quickly what I could do and how to do it. I knew that I just killed a shark so I knew I could open my inventory and increase my damage. And while I was there, I checked my health and could heal. if I didn't have fish chunks, I could just fly around until I found some little fish, shoot them and I'd be good. Then I knew I could just fly to another planet once I finished this one to get more stuff. Some games (especially game jam games) you get too many mechanics and just end up forgetting about them, but each mechanic here seemed necessary and you used it when you needed to.