David Hume, it is generally agreed, was about as attractive a man as ever lived. He had a gift for friendship, he was witty, and he was kind; he inspired almost universal affection in people he met. This is an affectionate biography of that man. However if David Hume had been only a genial buffer from Edinburgh, then 250 years after he died there would be at most local antiquarian interest in his life. But Hume was not just a genial buffer; he was intellectually threatening; that he was a genial buffer was incidental. Peter Gay wrote in his history of the enlightenment that 'when Johnson and Boswell talked about him, they talked about him with an unphilosophical aversion that smacks almost of fear'.
You get very little feeling for why Hume was so threatening from this book. You get the man, but you do not get the philosopher or the historian. You are told that he was not quite an atheist but that he was an honest man. But there is no adequate explanation of why someone supposedly shouted that out at his funeral, or why his family felt that an armed guard was necessary on his grave to prevent it being desecrated. The problem is that Graham is not really sophisticated about either philosophy or historiography. He dismisses Berkeley, for instance, as a comic footnote to philosophy apparently because he finds Berkeley's idealism ridiculous. He seems not to have realised that comic footnotes to do not get extensive discussion in randomly chosen one-volume histories of philosophy (you may not accept Berkeley's brand of full-bore subjective idealism but finding a flaw in its intellectual defenses is a serious philosophical challenge). He does not manage either to explain why Gibbon felt that a letter of praise from Hume on the first volume of the Decline and Fall more than balanced ten years labour. And finally, in spite of a final chapter dedicated to the dialogues, he does not really come to a clear position on what Hume believed (it is too easy to say that Hume not an atheist - after all by some definitions Benedict Spinoza was not an atheist either - a careful discussion in the Cambridge companion to Hume ended up labelling him an 'attenuated deist', which seems about right to me).
It is far too many years since I read Mossner's biography, so I cannot compare the two, but I think the world is still waiting for an up-to-date Hume biography.