I've got to admit, at first i was skeptic because I thought it was going in a certain direction for which I though some of the details where a bit too on the nose, but it actually ended up being a very pleasant gameplay! I really like the idea of exploring the mental degradation of the main character, and while I often prefer my supernatural explained, leaving the creature, and causes of the hallucinations ambiguous, actually did a great service for the atmosphere.
Overall, I commend you for the interesting concept and great atmosphere! One thing I'd point out tho, is that I'd tone it down with the creepy notes in the bookshelf, for example, a few come a bit too on the nose, and kind of drag me out of the atmosphere. I'd also suggest looking through true crime documentaries (as long as they dont make you uncomfortable of course): I'm a sucker for policial and horror media, and true crime history is a very good source for ideas and plot devices in such genres.
Overall, I commend you for the great game! I look forward to more updates.
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Thank you for the detailed feedback, the kind words and the constructive criticism! I'm glad that you liked the game, and I appreciate your advice! I'm an avid reader, so I'll be sure to check out some if that true crime stuff (probably books more than documentaries, though). While I draw a lot of inspiration from-surprise, surprise-horror and the occasional mystery, researching the methods and motives of real killers could lend a lot to the story!