This is a really beautiful game, I found the patterns in the architecture especially striking.
Also the way the flames are animated really stood out to me, as well as the flags in the final room. Taking the time to make so many different versions while keeping the movements similar enough that they all look like they're being acted on by the same winds was fantastic attention to detail.
The music is a great fit too. Tense, crushing stillness is the atmosphere I always imagine when I picture Carcosa and I think the music really captures that.