I very much enjoyed the character-building, which was subtle but showed the growth of our protagonists. I loved the dance between Red and Blue throughout time and space, and the world(s) in which they separately live and work. No part of the story was overdone or heavy-handed, but everything was aching with meaning and pulled me forward throughout the story (even when it was backwards in time). The writing was beautiful - clear but poetic. I very much enjoyed the world-building; it is a classic example of showing the difference between the reader's world and the worlds of the characters by natural mentions within the story, not exposition drops. The finale was well worth waiting for, but I won't spoil it here. A lovely read all around.