This one was a fast paced, but good read. The main characters, Red especially, imo, have a fleshed out personalities. The setting is intriguing and the glimpses that you get of it are fascinating. Plus the ending ties everything up nicely, pushing the theme that people perpetuate their own futures no matter what we do to change them - a "it was always meant to be" vibe that can have you question if there is true agency or not.

Only complaints are that it's pretty repetitive with the back and forth letters, the lack of setting information and just general motivations behind the worlds' forces (because it seems like it'd be SO COOL), and that in place the prose can get really purple to the point of annoyance. Easily overlooked stuff considering the book's length.