That's a really good concept ! That remind me a lot of subnautica, but in 2D ;)
The things that I liked :
- Building pipes was really fun, I think you should more concentrate on that
- Getting gems in the ocean, going deeper and deeper with the upgrades was cool
The things that you can improve for maybe a released game :
- The movement and controls, by manipulating character we feel like moving a huge spaceship, I know that the boost thing come from the theme, but it can be improved (by adding a better acceleration with a greater damp for example)
- The graphics, it's not your fall we are not all good at that, but consider asking someone to do it, or maybe just play with the post processing of the engine, light, shaders...