Marius has every claim to being an expert on More, and the comprehensive of the biography leaves little to be desired. The book is now 35 years old, and some of the trends among historians are evident in the biography: easygoing psychological speculation, a widely assumed theory of secularization, a blithe sense that religious earnestness of a certain sort can be characteristic only of modern fundamentalists.
Some themes get tiresome and leave you without much insight. Marius insists that More's lifelong regret of not becoming a priest or religious (if such regret existed) explains all of More's bemoaning the futility of earthly affairs. ('Perhaps More here vents his frustration that he never became a priest.' Or, notably, More's last days, alone, without kith or kin, no books, nothing: 'Now More had what he always longed for, the monastic life.') The fashion of the time, it must be, explains Marius's recurrent use of More's energetic and repressed libido as an explanans for a range of phenomena: his hatred of Luther, his non-mentioning of his second wife in certain letters, and so on.
Most of the book, in recollecting More's literary and political career, leaves you with a sense that Marius finds More a petty character, too given to fury over small matters, too aware that flattery might be effective. And if you're like me, these leaves you wondering why exactly Marius finds More so engrossing. I like hagiography as little as the next fellow, but the labour involved in bringing forth such a thick life of a figure so apparently un-magnificent is perplexing. The last two chapters do change tone; there Marius becomes slightly less critical of the 'hagiographical' sources we have of More's last days, and Marius seems genuinely impressed, even if puzzled, by More's martyrdom--his performance, as Marius would say. If you have Bolt's play and Marius's biography next to each other, Marius seems the less clever, less genuinely insightful interpreter of More's life. Bolt, an atheist, nonetheless seems more clairvoyant about why he is drawn to More.
Much attention is given, as is expected, given Marius's expertise, to More's treatment of heretics in England. By my lights, More seems utterly unexceptional on this score: that is, he made decisions, in his offices both as judge and chancellor, that we cannot but find abominable today but which were hardly uncharacteristic of those who held such offices in his day. More did not abuse the laws of his country; he used the only ones they had--bad ones.
I cannot rate the biography very highly, but it did not disappoint me in this respect: I was not looking for hagiography but rather for a biography that would give More a hard time. I suspect historians today might have fewer blind spots than Marius did (the ones mentioned above), but if no one has undertaken to write about More's whole life, one cannot go too wrong in reading Marius's life.