Ultimately a very typical denpa in both the good and the bad, but what it does well it does solidly: The psychological horror/first-person writing is really evocative and your perspective is an interesting one to occupy and piece together throughout, the ambiance is pretty good even if the music is lacking, and in general it just pulls the "can't take your eyes off" mystery vibe excellently. The character writing, with one exception, is pretty solid too; they aren't pure 'worldview'-type characters, all feel like true people.
Impossible to talk about the bad parts specifically without spoilers, though, so be warned. (spoiler-free verdict is 'go read it it's free and short and mostly good)
What it does less well is at least mostly contained, and all are classic things you wave away for the usual denpa anyhow. The inevitable more conceptual/sci-fi turn that murks up the psychodrama and strains credulity being the biggest and most classic issue, and here it's basically fine, shoved all the way to the end just to get the story's message across most directly, decent coda even if of course underwhelming in comparison to the beginning. Every time I read a sentence about the 'mechanics' of the world, the classical denpa heart weight was suddenly dropped for a slightly annoyed squint. That stuff shouldn't be there, there's no point to it being there.
Mostly, the whole 'amor fati' thing felt kind of underexplored, which is a real shame since it's such a big moving part on the first two thirds. Yes, at the end the world dying and her being the last one to hold out because of this love for the world while not loving living in it is a beautiful and nice send-off, but I feel like it didn't really investigate this tension as much as it should, it mostly just presented it and the contrast for you as the reader to reflect off of. Which is fine, I guess, but at the end I couldn't help but feel a little dissatisfied with this. It has all of that nice psychological tension and philosophical undergird and then it swings that into "but what if the main character's metaphysics were actually correct about the world", and, I mean, it wasn't the worst way for this to go but among the least interesting. Lacking follow-through.
Which is to say, strangely, it could do with being longer. Only a little longer, though. Possibly the biggest point in its favour is its pacing: it does a hell of a lot right for only being 4-6 hours long. To me this is its most remarkable achievement, even if it comes at the cost of the bigger ideas being inevitably left for 'interpretation' (read: underexplored and gestured at). So, all in all, a solid effort; nothing too unique but an unusually sharp, mostly no-frills execution for the genre. Worth a read, especially since it's free.
