Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
With Humbert as our controlling (and insane) narrator, the tone comes across as sly, superior, darkly comic, and intellectual, alternating between bemused weariness and sweeping romanticism. With very few emotional outbursts, Humbert's narrative remains cool and detached, amused in spite of itself. Humbert expresses both shame and bravado (I got her! I'm such a pig – my bad. But I'm the man!).
His constant addresses to the reader are difficult to take seriously, given that they are often followed by detailed exemplifications of his vile behavior. These addresses become failed efforts to set a tone of sympathy, to draw the reader into his point of view and thus to pull back our attention from the juicy story and consider the profoundly disturbing moral implications of what we are reading. In other words, if we like him or are like him, we won't condemn him; he thus uses tone to seduce us, make us comfortable, saying sit back and enjoy the ride. Humbert's dark humor and wit also serve as part of the narrative's smoke and mirrors, seeking to erase some of the horror trivializing the subject matter by offering jokes where shock may be more readily expected.