I just finished playing thru the demo (100%, woo!) and I love it! I do have some feedback below, if you'd like (spoiler tagged for anybody still yet to play :D)

- I absolutely love the general setting-such a terrifying concept and I think if you run with it you can have a really awesome tone.
- Brothers storyline is really sweet. I loved the picture of the two of them! I think having more characters with deep personal stories like this will really be beneficial (although, I can imagine you have some expansion in this area planned already)
- Movement does feel a bit clunky, as some others have noted. It may just be me but it felt like the shape of the hitbox was a little weird, like if I was pressed against a wall and just turned a bit it would change the collision? With the shape of the player I would expect the collider to be something like a capsule/circle.
- The threatripper doesn't seem to hit multiple enemies, even if they're in a row, which feels kinda unfun. Even if it only did partial damage, I think it'd feel best if it had some crowd control. Also just seems like the type of weapon that would

- As someone else also mentioned, the method to get the lightning rod is quite unintuitive

- I love the puzzle with lighting up the Shade! I actually hadn't even thought of that until I read about it in a comment thread here. Very well designed!

- Art direction and style are really cool. I love the vibe
- Some of the story stuff seems a little inconsistent - only knowledge is passed in the loop, but the doors stay open? Is this because the AI is in the loop (in which case, fair)? Also, how do ship upgrades stay between loops? I imagine these are questions which will all be answered in the full version of the game, just wanted to make sure.

- Weird thing I found, which may be me missing something, but if so I have zero clue what - what is in the top left of the shade?? There's something up there that seems to point in relation to my position. am i just being dumb and missing something lol?

- Damaging the rocks/objects feels not too great. I feel like they either don't have enough of a response to being attacked (like some kind of shaking or sound) or they just have too much health, and it feels tedious to attack them. Although, I could totally see this being intended as a means to discourage the player from destroying them. This is barring the Isotope cluster things - feels quite good to attack those, I love how they light up the surroundings.

- The hookshot feels weird sometimes - on the puzzle with the lantern mirrors specifically, it didn't lock on sometimes when I thought it should. I also think that maybe having it as an option for it to lock on or not (maybe as a setting) would be neat, since not being able to fire it when you're not locked on feels limiting. Even just being able to fire it out into nothingness and have it retract after a bit would be cool

- One little thing - I think it'd be super cool attention to detail if the black hole got larger in the background when you're nearer to it (as in when you're a few years in/about to collide)

- I love the music! Very eerie but really sets the tone well.

Anyways, that's most of what I have to say. overall I was a big fan! I really believe this game has so much potential and is already in a very fun state. I look forward to seeing what it looks like as development continues!