I think one of Lolita's greatest strengths is its ability to humor and entertain the reader while also remaining essentially tragic at its core. I know Humbert is basically a monster and an unreliable narrator, but his obsession with Dolores and the way he breaks her life just tears me apart. Anyhow, from a technical aspect, I think the novel is nearly perfect, and I'm a sucker for the flowery language. Also, I find it interesting how Nabokov, as an "outsider" to America, was able to capture its essence so well.
By the way, have you read any other Nabokov? In some respects, I think Pale Fire is a better "novel" (I use the term loosely), but Lolita is still my favorite.