Hey man, you got some really cool stuff going on here.
I love the atmosphere, and the level details. It was a real pleasure just being in the environments. Really digging the vibe, especially in the lower parts of the second level. Nice job dude.
I'd also like to praise the animations and look of the weapons, i think they're quite nice. I wouldn't object to an old school (Doom, Quake 1) POV option for the weapons, but i'm getting ahead of myself. Being able to throw the Katana was a very cool touch also, though i only found myself using it against the larger enemy variant.
Also, i'm a fan of how you used ambient noises instead of a song, until the showdown in level 2, where the fight music kicks in, to really give it more of an impact.
I'm sure you've thought of, or taken in to consideration most of what i'm about say, but i figured i'd give you my immediate thoughts on what could be tweaked or changed after playing the demo.
- I think the game could benefit from having a slightly higher movement speed. So the game definitely has a horror vibe to it, and i assume you don't wan't players to feel too empowered. But i found myself getting very frustrated when i got lost, and had to search around the levels, due to not moving as fast as i'd liked. I'm sure it's a tricky balance to get right.
- Thoughts on dashing. So i LOVE dashing as a mechanic in fps games. I think it can really at layers to the gameplay, and i'm happy you've incorporated it as a core gameplay pillar. I'm not sure if this is deliberate or not, but dashing really only feels reliable in the air and not as much so on the ground. I mean yes, it WORKS on the ground, but the distance seems to vary quite a bit, sometimes my character barely moved if i didn't also jump. It just had an unsatisfying sense of momentum to it, and a feeling of inconsistency. I´d much prefer if the dash length was a fixed distance on both the ground and in the air, or if it was just fixed on the ground, and in the air your momentum would still carry you forward after the dash itself has ended.
- The game might also benefit from having switches and ladders colored or lit in a way that stands out a bit more. I definitely didn't notice the first ladder in the first mission by the fence, with the switch behind it. I ran around for quite a while before spotting it. The same happened with some switches.
- In the lower parts of the second level, when the music kicks in, and there's a few waves of enemies to fight, i noticed that you take damage from standing on the red grates on the floor. I took me a while to realize why i was taking damage. So i think it might be good to communicate more clearly in-game that those things damage your health. Or just not have them damage you idk.
- I definitely understand why you WOULDN'T do this, but while playing, i did think to myself, that a flashlight or lamp mechanic might be beneficial. Some of the areas are very dark, and i had some trouble finding my way around in them. Maybe if you couldn't use weapons while holding the lamp, it'd fit with the vibe and balance of the game. Though honestly this could be dealt with a dozen other ways, and might not end being an issue when more video settings are added.
- In the second level, i ended up getting stuck in this spot. With no way to get myself free. It might be a good idea to add an invisible wall here, so that players don't get stuck. 
Anyway, those are just some thoughts. Really enjoyed the demo, and i can't wait to see how this turns out. Good luck finishing this thing.