Mendelsohn makes the case that Sontag misunderstood her own strengths (as critic versus novelist) and affiliations (with the eighteenth century rather than the nineteenth):
This journal reveals a person for whom, however much she saw herself as a sensualist, the cognitive and the analytical invariably dominated the erotic and the affective. ("Emotionally, I wanted to stay," Sontag wrote of her decision to leave home and family in Los Angeles for Berkeley. "Intellectually, I wanted to leave." She left.) The inevitable triumph of the head over the heart in these pages defies, I think, a description of his mother that Rieff gives in his preface. In speaking of Sontag's extraordinary literary ambition, he compares her to Balzac's Lucien de Rubempre, the hero of Lost Illusions, the talented youth who comes from the provinces to find literary fame in Paris: a comparison that concludes with his summary explanation of Sontag as a "nineteenth-century consciousness." It is a judgment, you suspect, with which Sontag, with her insatiable avidity for experience and her penchant for the Continental novel as model of the highest form of literary activity, would have concurred.
And yet when you survey her career with an eye as coolly dispassionate as the one she trained on so many objects, it becomes obvious that, temperamentally, she belonged to another century entirely. Her failure to understand just which century it was accounts for the sense you often get, taking the work as a whole, of aspirations that were at odds with her temperament and her talent; and it explains a great deal about both the strengths and the weaknesses of her work, and also the strange fascination that she exerted.