Awesome game! Feels like a minimalist Subnautica. I love the tension between wanting to explore and go deeper, but needing to surface for oxygen.
One thing I would love is an indicator for the shop location, and I think the pipe placement system could use a bit of polishing. It's hard to tell what my max placement range is. But once the pipes are placed, it's a really cool system.
It seems like the acceleration is capped, but I think that a player willing to spend a lot of oxygen quickly should get rewarded with more acceleration than is currently allowed.
I also think some basic sound effects would really add to the liveliness of the game.
I love the darkening of the water as you descend more and more.
I also think the level of difficulty is pretty good. Gems are hard to reach but feel very rewarding. And death seems appropriately punishing. I got kind of stuck in the progression though, possibly because I threw away too much money on dangerous trips downward, and gems are rather rare. Do gems respawn if you die while holding their money?
All that said, great game! I had a blast playing it, and I would love to see more.