Awesome vibes! The atmosphere is great, loved it. Felt on edge the whole time, even though in hindsight the actual enemies were rather simplistic and not much of a threat. I sadly only found one half of the new weapon, and I'm curious to know where the other half is and what it does :D
I love the story telling and the world you have created. I think the crawling of the lava and water world could be expanded a little, and that would be my main critique. Combat felt a bit weird with the camera snapping, which then stays in place until you rotate, but that's only a minor thing.
Also, when the game loops, the inventory and planets don't reset. Not sure if that's intentional or not. At first I thought there would be another twist coming when playing through it again, but on the mining world the puzzle wasn't reset so I checked the comments here to see if the game actually ended or not. So that's also something you could improve to make it more clear to the player.
Overall though, excellent game!