I am afraid I am going to have to be a little hard here and say this barely scraped 4 stars for me. The middle really dragged. I can't really explain why without going into spoilers (which I am not a fan of doing in reviews). I will say that there wasn't the same sense of progress that you got from the first two books. A sense of something new developing. The middle third is very focused on a (to all appearances) regressive setting, thus the sense of the new wasn't there for me for a good chunk of this read.
The ideas are still top tier. The book started well and the ending was satisfying. Maybe it needed a tighter edit, maybe I was just not in the right place for this.
Still, it is Tchaikovsky and my reservations could just be a me thing. It's still at least a 4 star for me so I can definitely recommend it. Especially if you enjoyed the first two in the series.