This question contains an interesting choice of adjectives, as some would argue that it is difficult for a work to be "fantastic" as well as "personal." Indeed, being "personal" might lend itself more to being "realistic" rather than being "fantastic." However, what it is clear that this novel does is present the reader with the perspective of a character that normally the world would shun and reject. However, in Nabokov's hands, it is clear that his anti-hero gains the sympathy and perhaps, the complicit acceptance of his audience, in spite of his crimes, and his inability by the end of the novel to fully accept the responsibility for his own actions. This is of course a theme that has dominated literature throughout the ages, with audiences being made to like characters and sympathise with them against their best intentions. It can be seen in characters such as Richard III in Shakespeare's classic history play, for example. This novel therefore presents in a very realistic way the thoughts and perceptions of a paedophile as he struggles to come to terms with his desire and what he has done. Note for example, the following quotation:
One moment I was ashamed and frightened, another recklessly optimistic. Taboos strangled me.
The picture the protagonist presents of himself being "strangled" by the taboos of society is one that invokes sympathy, and his account in this novel, upon reflection, shows mastery of language in the way that Humbert uses it to disguise and cover up the reality of his actions. What is realistic about this novel therefore is the way that the power of language is presented to make the unforgivable forgivable and actions which are seen as being "beyond the pale" acceptable. There is nothing fantastic about this and the reader ends the novel having been thoroughly seduced by its protagonist, against their best intentions.