Solid style, solid controls, solid demo.
You have heavily referenced Metroid and take a lot of 'the good stuff' but also taken other scifi influences and they are coming together nicely.
Hooked it up through steam on a windows machine to try out the steam controller and it is pretty good. Takes a few seconds to detect the controller at startup, and if the controller ever disconnects you have to restart the game to get it back. These are pretty common issues with controllers, so are at worst C bugs.
The diagonal angle fire is a little wonky feeling, but I imagine you get used to it with longer play. You might consider keeping the character facing the same direct when moving and holding an aim button so the player can do some backpedal firing and can also target switches a little better.
Less technical notes:
I am interested in what other elements you plan to include. How much are you planning to diverge from Metroid and what kind of story you plan to tell. (I am not asking you to answer any of that, I am just saying those are the elements that would excite me most about the continued dev on the project)
They are small touches, but the reflections on fluids and the little light enemies go a long way to pull you into the game.
Likewise, starting out with nothing instead of starting out all power armored up feels like a better plot piece. Others have already spoken to progression and it sounds like you have some ideas about it, so I will just note that you have made the first part of the game feel almost more like alien isolation and then you get to build up to being a force of your own. It feels good and has a LOT of potential as an immersive experience and I hope you find the balance you are looking for there.
There are also a lot of teases of lore and you figuring out what has happened to the base. That is an aspect I would love to see leaned into. The little bot at the beginning who gets you started is a beautiful little touch and you have other ones scattered about as well(like what appears to be a corpse of another female who looks very much like you as you flee the first section.)
All and all this project feels like it has a great deal of potential.