this was a really great demo, and you've definitely made me intrigued for the full game! :D
i really like the vibe of this place. it feels so much like i'm walking through an old, labyrinth-like, gothic castle. the dark walls of the hallways contrasted with the vibrant carpets really gives off a feel of "place that's trying to give you the illusion of elegance, while being clearly abandoned and destroyed". it reminded me of castlevania haha. i also really like how there's different floors, each with their own style; ones with carpets and generally nice looking aesthetics, and one that looks more like catacombs, gray and dreary and run down. and the cherry on top is the way the rooms light up when you enter them, i LOVED that detail and i have no idea how you did it but it was so cool haha. overall the visuals/presentation are great, and really effective in conveying the feel of the game!
i also really liked the writing. love me some verbose, old-timey conversations lol. i like how everyone seemed to want to one-up each other in logical reasonings, it fits a lot with the writing style of the time. the word choice in a lot of places was extremely good, and every time the writing turned to lyrics, my eyes were glued to the screen. those moments were incredibly well written. i'll admit the writing style made it a little hard to follow the story, but i liked how it made me try to piece everything together so i could understand the full plot (from what i could gather, these two men were once friends, but their friendship was torn apart by their mutual love for a woman. she started a relationship with the antagonist, but he killed her when he found out that she only wanted to be with him to be immortal. maybe i got everything wrong, feel free to correct me haha). i really like how you interpreted the theme too, not necessarily by having the devil as a character (or maybe the antagonist is the devil), but the themes of corruption and evil that are associated with him in the dialogue and plot. it's really clever! (also i didn't know where to put this but i loved how the text in the menu ui is changed to fit the setting, such a neat touch :>)
i feel like at some points it was a bit hard figuring out where to go. the maze-like hallways are a cool aesthetic but they're kinda hard to get through, especially with so many ghosts roaming around; and the rooms being dark before you enter make it difficult to remember what's inside each. maybe the items/stairs of the rooms could be visible even if the room itself is dark? and just before the ending, i entered a random room and it suddenly took me to the final part. i would've preferred if there were some stairs or something like that, just to bring attention to that room. that's just my opinion tho.
overall, this is a pretty great demo and a really intriguing showcase of what to expect in a full game! good job!! :D