Really engaging -- I liked the portrait of Justices Jackson, Frankfurter, Douglas, and Black very much. It was also striking how incredibly petty their vicious disagreements were. Sometimes I felt like I was reading a mash-up of a history of legal intellectuals and a really lame episode of Real World: Washington, DC (or an episode of Full House where people decide that maybe it's not worth it to forgive each other's minor faults, after all).
Having seen as a law student where these justices were at various points in their careers, this book was really helpful for knitting together their stories into a narrative. It helped me see the evolution of Black, Frankfurter, and Douglas in particular.
Lots of interesting anecdotes throughout the book, also.
Sometimes the focus on the justices (and FDR) was almost a little too myopic -- cutting away from Nuremberg to illustrate Jackson's disappointment at not being named Chief Justice is one thing, but I thought it was striking that we never even got a narrative of how things ended at Nuremberg.
All in all, though, a really fascinating book and one that gave me insight into both the New Deal and the development of 20th-Century constitutional theory.