This book is everything I wanted and expected, plus so much more! 
The progression of Bastien and Ailesse’s relationship is perfect. I love enemies to lovers when it’s done well, and this was definitely one of those times. I think they’re personalities perfectly complement each other, and the way they so gradually and reluctantly fall for each other is so well-executed and believable.
I also really enjoyed the lore and magic of this world! The concept of the souls of the dead being a color regular human eyes can’t see and the grace bones of birds giving the Leuress the ability to see that color is so clever and unique! Plus the grace bones are such an interesting and cool idea themselves! Killing animals to receive their special abilities by wearing their bones but only receiving those graces if the kill is honorably performed and with pure intentions is just amazing, though killing animals is never exactly pleasant to think or read about.
The mythology and gods of this world is super interesting, too. The story of Tyrus and Elara’s love, their banishment from one other, and the resulting Underworld and Paradise, plus the connection between the myth and the main plot, was so fascinating to observe. 
Also, there are some plot twists that I did not see coming that really took this book to the next level and made it something so unique! I loved this so much and can’t wait for the sequel!