Pretty fun game! I kept dying early on because I found the submarine to be pretty hard to control; it feels too heavy, in my opinion. I saw that there were sonar and mobility upgrades, so I'm guessing the mobility upgrades would help make the submarine feel less heavy, but I think it would've been good to make it easier to control from the start so it feels a bit better to maneuver.
The sonar idea is pretty cool though, I like that it lights up the obstacles in your path, as the game is pretty dark overall as you sink deeper, so it clearly shows you what to avoid and collect. Great job on this!