Since you were asking for an honest review I'm going to includes scores and pretend I was a judge haha!
Definitely some cool ideas here. Being totally surrounded by darkness, and absorbing darkness juice to use as a resource is very neat. Having combat with anything other than the most basic of enemies being brutal is also something that brings out the horror aspects a lot here.
For theme, you definitely got the shadows part down, but I think "absorbing shadows to transmute them into upgrades and abilities" is a bit of a stretch for alchemy. The shadows part is done well enough though that I think I would give you a 3/5
For Artistic Style I think all the backgrounds and sprites look pretty good for whats there (keeping in mind this is supposed to be a prototype of a game). I think it falls a little with some of the UI. The extra bit of line work and filigree you've added to all the boxes in the UI don't feel like they mesh with the spooky aspect of the game. Specifically the extra bit of detail around the health bar meant I didn't grok that is was a health bar until I got a health pickup. 4/5
For Cleverness I am only rating on mechanics, not on story as I didn't complete the game (we'll get to that in a second). Mechanically this is a pretty bare bones traditional roguelike/sokoban-esque deal. I got to the point where I had two abilities, place darkness and shadow strike. Place Darkness is definitely interesting and there is a lot of design space you can probably (and maybe already did). 3/5
For Playability I think there are a couple of issues. Firstly there is a lack of checkpointing. Getting killed by the big giant enemy is very easy to accidentally do. The exact tiles that will kill you aren't immediately obvious on first playthrough and there is no prompt to the player that forces them to consider what they are doing. That would be fine if it didn't make the player spend 80+ turns (I counted) going back through that first section again, picking up everything (including the secret) just to get back there. A simple checkpoint after escaping the first Hand Eye Coordination monster would prevent this, and while it would mean it would lessen the fear of death to some extent, having to repeat moves in a more puzzley game like this is extremely frustrating. This is the reason I didn't play the game to completion.
The second issue has to do with memory. Having to memorize a maze is not particularly exciting for me to have to do as a player. Implementing a fog of war that is permanently lifted would make this not be an issue. You could still have the darkness by making tiles not in line of sight very dark, but being able to see where you've been is more annoying than anything else. Playability 2/5 with the caveat that it would be very easy to fix these issues and bring that score way up.
Unsolicited Ideas Time. Playing around with fog of war is super interesting. Instead of having Darkness Juice™ just lying around, you could have exploring the fog of war directly fill the darkness meter. This would make the player more careful about moving super quickly because they wouldn't want to "waste" the darkness. If the player has collected all the darkness but have actually wasted enough of it that they can't advance, then a checkpoint could reset the fog of war in an area. If you were to implement the more permanent fog of war I mentioned, you could even have set sequences where returning to a place you've already explored is now suddenly different which would add a very spooky section.
This is probably way more review than you wanted, but hopefully it isn't terrible. I think your game is fun with some frustrating points that could easily be ironed out. Have fun out there!