There are four things that make a good book: good plot, good ideas, good characters, good writing. In "Breach", Peper has two, at most three.
Plot in a nutshell: Emily Kim, former hacker and social engineer, haunted by her demons, returns from a stint as a pit fighter in a tropical backwater to save her former street urchins (now masters of the universe) from a dastardly plot to overthow the tech utopia they created.
If you feel the impulse to yawn, don't stop yourself on my account.
On the plus side, Peper has some real insight to offer into the future of our tech-soaked society, and it's baked into this book with skill. However, this insight is not nearly as ambitious or as intelligent as Piper thinks it is. It can't hold a rusty candle to Gibson or Stephenson. The Commonwealth and its feed are the most potentially interesting parts of the novel, and Peper spends very little time on them.
The reason why, and why this book is so mediocre, is that Emily Kim is about as interesting as a bowl of oatmeal. Granted, Peper commits no major crimes in drawing his female protagonist, he fails to make her memorable or interesting. Her moral anguish feels overplayed, her redemption too easy, her brilliance overstated. Emily's supporting cast adds next to nothing, mainly paper-thin bit parts for Emily to punch, pontificate, or apologize too.
For all we know, Peper has created a grand vision of the near future, complete with a market-based solution for climate change... But we'll never know it, because we get to ride with Emily for a brisk 220 pages and spend 140 of them on her inner life. I want to hear more about that vision, and less (nothing, if possible) about Emily. Yet Peper clearly loves Emily (if his self-indulgent afterword is any evidence) far more than he wants to share that vision with us.