Really nice game. My favorite moment was when, after I had bought all the upgrades but the last, I finally started to explore the actual geometry surrounding the level. It was a huge change in pace--I no longer cared about the minerals whatsoever, and instead only about the actual environment around me. It was a cool moment because the actual setting of the game had seemed to be almost meaningless for most of the game. The fact that it was set in the ocean was arbitrary. But when I finally just stopped going after the metal so hard, the ocean environment was quite meaningful. And I think the abyss part of the environment really nails this. There is no ore in the abyss. The only reason to go in there, aside from the narrative one, is to see the environment itself. I don't know, it was just a nice thing.
Aside from that, the core gameplay loop was very nice. The upgrade system worked really well. Having ores that become increasingly valuable that require increasingly better equipment is just a really nice way to build that kind of upgrade-loop system. One aspect of it that I especially like is when you get just a tiny bit of the ore at the next pressure level. It really motivates you to want to get the pressure upgrade for that level and get the hugely increased cash flow (which, of course, will shortly be matched by hugely increased upgrade costs).