Overall very engaging and well-made, highly polished experience. 
I'd only add a few things:

Some of the spectre's appearances (for me) occurred in too quick succession to keep their edge and the ones that appeared shortly after the first really didn't do anything. Also, on two occasions -- both in exiting the doorway to the right of the stairs -- the entity remained for quite a while and let me walk right up to and through it and look at it for ages which sort of took away the mystique. 

The textures on the entity's model and the initial 2-D flash on-screen are a bit too stylised to not seem cartoonish, especially given the photorealism of the rest of the setting. I'm not saying stylisation and even cartoonishness is bad, I just think in this case it looks a bit out of place.

I found the lore interesting but a bit confused but I feel like that's just me not getting it, I'm probably going to replay it and examine it a bit to get what's going on.

EVERYTHING else was great, the only issues I can think of really minor -- like you could just ignore everything I've brought up and still be left with a pretty top-tier piece, they're really minor; I can't emphasise enough how little I think there is to be improved on.

Random praise: The camera's motions are really organic, I think its' delightful how it doesn't just pivot statically with the mouse and instead has some kind of inertia with how it rolls a little when rotated. Also that one portrait with the face was legitimately more unsettling than anything else that could possibly come after. I'm serious, that wall art will be with me forever.

Anyway. That's that on that. I'll be looking forward to what's next -- 5/5 :]