I have reviewed the author's work previously, so when he offered a review copy for this book I was happy to accept!
This book vacillates between introducing incredibly clever sci-fi ideas and struggling to develop those ideas adequately. A man sending his 50 something year old man back into his 8 year old body and living through his youth with the memories of what happened. A time traveler writing a massive series of books about the future that unintentionally creates a secret organization. A cult using wormholes to tether it's followers together for the benefit of the leader. Governments using images from the past in it's court trials and trapping human minds in technology to power AIs. They're all incredibly interesting ideas... but there's just too many of them for any one to have space to breathe. As a result, they're introduced quickly... and then the plot moves on.
The linear-yet-not format of the plot also has an effect on the book's coherency. The idea is an interesting one in itself. Go through the timeline of the world in literal chronological order, from the pre-historic to the far future, with time travelers popping in and out. It is linear on the large scale and non-linear on the personal. But combined with a gigantic cast of characters and increasingly complex technology that requires deep explanation, it creates an incredibly confusing series of events. The most obvious sign that the narrative struggles to explain itself is the fact that there's an appendix at the end just to lay out each character's arc clearly.
Like the many story ideas, the character themes also had incredible promise... and there were also too many for any one of them to have real space to breathe. I would have loved a deeper look at Mitchell trying to avoid the marriage that ended in divorce, but falling in love with his wife again anyway. Or Willy facing the full terror of knowing his children would go through the horrors of history he knew were coming and the cult that grew because of him. Or Cassandra's growing desperation as she tries to change the past, but never can. Or the many characters whose moral compass' grow twisted as their time-based inventions gain them money and fame. Or the whole host of characters who exist only for a couple segments before the subplot they're in ends. All incredible character ideas, all given only minimal space to make room for the rest. As a result, there are several gigantic emotional beats, but the reader isn't given the space to actually feel them deeply.
The best way I found to read this book is to view it less as a novel and more as a short story collection. While I would have preferred a more in-depth focus on fewer ideas, it's still worth the read for the creative sci-fi concepts alone.