I can't address the potential theological and historical miscalculations in Metaxas' biography, but I found Bonhoeffer to be compelling because of the story it tells of a life of vibrant faith in turbulent, dangerous times. Dietrich Bonhoeffer lived in Germany during both WWI and WWII. He knew by the time he was thirteen that he would study theology, and as an adult he pastored churches, trained young pastors, and wrote prolifically about spiritual topics.
Dietrich Bonhoeffer's life story is replete with educated, accomplished, and influential figures: His father was the chair of psychiatry and neurology at the university in Breslau; his brothers excelled at law and physics; he counted among his friends, acquaintances and colleagues Bishop of Chichester George Bell, influential theologian Karl Barth; Martin "First they came for the socialists" Niemoller, pastor and theologian Franz Hildebrandt, and his best friend and biographer, Eberhardt Bethge. To read Bonhoeffer is to encounter the dominant thinkers and sculptors of 20th century protestant theology; and Metaxas weaves these characters into a detailed yet coherent and absorbing narrative.
The book's portrayal of the plot to assassinate Hitler is action-movie material; no doubt someone has already acquired the rights (Sean Soul Surfer McNamara? David L. To End All Wars Cunningham?). Bonhoeffer himself was never the guy in the room with his finger on the trigger --but his collaborators were; and Metaxas' detailed chronicle evokes suspense and intrigue.
I admire the Bonhoeffer that Metaxas depicted, but I began to wish for a bit more transparency around Bonhoeffer's struggles with sin. Was he ever lazy, selfish, or proud? Did he ever have one drink too many, or get angry or defensive? Did he ever swear, or cut someone off in traffic?
There is one account of Bonhoeffer regretting and repenting his behavior: He was asked to preach at the funeral of his twin sister's Jewish father-in-law, and sought the advice of his district superintendent because the decision was fraught with social, political, and religious ramifications. A few months after he declined, he begged forgiveness from his sister and her husband, writing "How could I have been so horribly afraid at the time?...It preys on my mind...I know now for certain that I ought to have behaved differently."
I found Metaxas' writing style to be occasionally lazy and distracting. He uses a limited vocabulary to editorialize unnecessarily. For example, "The three lectures are impressive, especially for someone only a few years out of high school..." Metaxas wrote, inserting himself as the arbiter of academic and theological value, rather than relying on an authoritative source. Two pages later: "Bonhoeffer's sentences could be impressive," Metaxas said; and in the next chapter: "...the list of speakers was impressive" at the funeral of his former teacher Adolf von Harnack. I began to think to myself, "Show, don't tell."
Metaxas' editor allowed him to get away with frequent use of cliches, a lazy device that a more dedicated writer would avoid like the plague (See what I did there?): "...(Bonhoeffer) ran a children's service, though this did not begin with the bang he had hoped."
He also writes as though he is an omniscient narrator who knows his subject's inner-most thoughts and motives; and I find this device to be untrustworthy in a work of non-fiction. For example,
On February 4, 1936, Bonhoeffer celebrated his thirtieth birthday. He has always felt overly conscious of his age and thought thirty impossibly old.
A new decree required all Jews in Germany to wear a yellow star in public. Things had now moved into a new realm, and Bonhoeffer knew it was but a foretaste of things to come.
But these criticisms aside, I would recommend Bonhoeffer: Pastor, Martyr, Prophet, Spy as thorough and fascinating story of an extraordinary, courageous, and faithful life. I think now I will read the original biography of Bonhoeffer by Bethge -- which gets nine five-star reviews on Amazon in spite of its prohibitive 1000+ pages.