If you have not played the custom story yet, do not read this comment. This is my impression on the story. Excuse me if my English is not always clear.
Well. I played a little, but I actually hadn't the courage to finish, not because the story was terrifying but because it became, in fact, quite boring and sometimes ridiculous. I will develop my idea and try above all to give you some advice. Even if I do not claim to know how to make a perfect story (mine is under development),I think I can help you a bit, as a player and fan of Amnesia.
• The story :
-The story was quite classic but interesting. However, I have not really been able to get into because most the notes you left were vague in a negative way, or vain. I think you should develop them a bit to create a true impression of realism. No matter what PDP'fans and others morons can say about it, what is more interesting, what is the most vector of horror in a custom story, it is primarily the story and how it is staged.
Neither jumpscares, nor monsters. It creates surprise, not fear.
-I really liked the Lovecraftian references and the fact that it was inspired by the Myth of the Al-Azif. But it's too bad that, (for me) it doesn't correspond AT ALL to a Lovecraftian universe. I don't know if you have ever read Lovecraft, but if you have, try to study the ambiance. It's very important. There is a strong power of suggestion.
-Each creator of custom history should ask this question. Why the character, facing such horror, does not simply escape rather than continue to face them ? In this case, why the detective does not leak to the sight of a monster, instead of going to the library (where he see a new one), and then decide to continue the adventure ? This is nonsense ! You should work on this.
• Scares/ambiance :
-It wasn't scary at all. I "jumped" several times, but never under the influence of fear. Drop a skull at the bottom of a staircase with a mocking laugh, open a door with a strange laugh, make a monster appear and then immediately disappears, does not create a feeling of terror ! Because it's just too much, so, in a way, ridiculous. The idea of dust falling from the upper floor was good. But at a such frequency, it becomes uninteresting. It scares me "Study of Insanity" and the original Amnesiae, because it had a specific duration.
-Too many monsters. Unjustified apparitions. Monster that suddenly get out of a room already visited. Several monsters at once, it is quite illogical and it has no value vector of terror. It is simply illogical and it means nothing. I do not particularly like that point. You must moderate their use. The best customs stories are those that combine idea that suggested terror with terror that we livedas players. Deterioration was truly awesome on this point. The monsters were quite rare, but the history and the environment, were disturbing. That's what gives us a sense of fear.
• Environnement :
-Work on the lighting in some room. Especially at the beginning. The fireplace light was.. Well, strange.
-Some walls are misplaced.
-There were however some environments pleasing to the eye !
I'm sure you can make an awesome second chapter if you put a great work on it. Good luck to you, and don't take all of it as an offence, it's advices. I really want an awesome second chapter !