Graham Robb is an excellent writer, and, in both this and his Hugo biography, has shown he is a great lover of classical French literature. While the Hugo covered the author's life, and his times, this Balzac mostly looks at Honoré and what made him what he was. I would have liked to see more contextualization, especially because Balzac's peak period of writing (the 1830s) was a time of turmoil and change in France. I was also surprised that Robb mentioned so few of the novels; he does quote liberally from a few of them, but barely mentions when the different works were written. This would have been a better way to place the works in the Balzacian timeline.
Nevertheless, faute de mieux, this is the best there is in English. It's surprising that, for an author who wrote so much, and for whom so many books remain in print in English, there aren't more biographies or general studies. The Comédie Humaine is one of the landmarks of world literature, and if you haven't read any Balzac, or if you have and want to learn more, this book will give you some great insights into who the author was. But it won't tell you very much about the works or fit them into a broader context. That book remains to be written.