Whether Proust's masterpiece surpasses Don Quixote or Moby-Dick or Anna Karenina (or its own near-contemporary, Ulysses) is a pointless question. What matters most is that Nabokov read Proust deeply and lovingly--with the eye of a master who was himself in the process of writing his greatest work, Lolita.
On the first page of Lolita, the narrator, Humbert Humbert, writes, "Did she have a precursor? She did, indeed she did. In point of fact, there might have been no Lolita at all had I not loved, one summer, a certain girl-child. In a princedom by the sea. Oh when? About as many years before Lolita was born as my age was that summer. Although the immediate literary reference is to Poe's "Annabelle Lee," in point of fact, there might have been no Lolita at all if Nabokov had not loved Proust's In Search of Lost Time.
The Proustian themes running through Nabokov's varied works--the themes of time, memory, identity, sensation, jealousy, loss, etc.--have long been explicated by other critics. But, it's only in the last hundred pages of Proust's final volume, Time Regained (the book that culminates the 4,300-page novel and that even few critics have actually read), that so many of those Proustian themes come together and create a new theme that Nabokov was to extrapolate to such an extreme in Lolita.
Humbert similarly forces the young "nymphet" Dolores (aka Lolita) to replay the role of his lost Annabel Leigh, who died soon after their youthful romance by the sea. In her book Reading Lolita in Tehran, Azar Nafasi writes astutely about how the tyranny of memory can be forced upon the helpless. When Lolita's mother, Charlotte (whom Humbert marries to instate himself in the house), dies (she runs out into traffic after confronting him about what she reads in his diary), her flight is an ostensible attempt to mail damning letters. But, her death could also be seen as a possible suicide. Thus, Humbert's tyranny over the girl-child becomes complete.
In the very final pages of Time Regained, the perhaps 50-year-old Marcel makes his preparations to withdraw from society and finally begin writing his novel. Before doing so, he asks the still living Gilberte (who has become unrecognizably old and grotesque) to help introduce him to young girls. Gilberte is the daughter of Swann and Odette, whose unhappy love story forms much of Swann's Way, the first volume of Proust's novel. Those original patterns of frustration and betrayal formed the template that the young Marcel would relive in his relationship with their daughter and then later with Albertine.
Marcel sees these patterns and realizes that real life could provide him with nothing but dissatisfaction. His only possible happiness can be in extracting life's essences and turning them into a book, so he makes this audacious last request of his childhood girlfriend--not because he feels that he can find love with any of these young girls. He is far beyond Humbert's stage of actually trying to relive the past with someone new.
The second volume of Proust's novel--the volume in which Marcel breaks with Gilberte and then later meets Albertine--can be translated as In the Shadow of Young Girls in Bloom. It's simply the bloom of youth that he wants to be near--to caress in his free time and to help refresh his aging senses as they delve into the deepest recesses of memory to create his book.
Gilberte's response to his request is beyond audacious. Unlike Lolita's mother, who may have chosen death when she discovers Humbert's monstrous nature, Gilberte perpetuates the past by presenting Marcel with her own teenage daughter. "I thought her very beautiful," writes Proust's narrator, "still rich in hopes, full of laughter, formed from those very years which I had lost, she was like my own youth."
The pattern now reset, this exquisite girl, this "masterpiece" of time, as Proust describes her, is now (like her literary successor Lolita) fated to relinquish her hopes, her laughter, her bloom, and the very time that her existence has allotted her to be young and free--all to a sick man obsessed with recapturing his own lost time.