There was so much I liked about this book: Stephenson's geeking, a fun protagonist, and a coherent plot that had a proper ending. I assume the latter points are due to his co-author. 
 That said, the book could have easily been trimmed in half with proper editing, and a lot of the story ended up being running up and down tunnels, chased by bad guys. The protagonist's field specialty (linguistics) was never really explored because she was so gifted at languages, she (and then it turns out others) could just pick up new ones in a few weeks. That's ridiculous and it stole from the much better plot this book should have had. 
 Instead we end up with scheming bitchy witches, casting-central idiot bureaucrats, ridiculous plots to "earn" unneeded money from treasure hunts while working within the military industrial complex, and an entire cast without inner lives or motivations beyond showcasing cool worldbuilding. 
 This book deserved a better book. It has so much of what I love about Stephenson (the geek dive) and it had the discipline, presumably from the co-author, to tell a complete story, but the story it told just wasn't compelling and the characters felt wafer thin. 
 I can't imagine how good this book would have been if it had gone through five or six more revision cycles that narrowed scope, got rid of the pantomime villainy at both ends of the timeline, and given each character depth. 
 Think "bad Connie Willis meets good Stephenson interludes"