Don't be juvenile. "The best novel of the 20th century" is excessive praise for Lolita, and the book, in spite of its good qualities doesn't deserve it.
The humor in Lolita goes well beyond topical jibes at pop culture (a culture which is much more prevalent now than in the Truman-era America he was writing about). It’s sophisticated literary wit: multilingual puns, references to all sorts of other texts. It was written nearly sixty years ago and has not really dated. As popular now as ever.
It is possible to have too much of a good thing, assuming it is a good thing. Read enough of Ada and you may not be so enthusiastic about Nabokov's "I am so clever" wordplay.
Nabokov is impossible to attach to any literary movements and thus is not dated by them
Nabokov's fans advocate a particular view of the novel that not everyone shares. In that sense he is attached to a "movement" of sorts.
It may not be the best of the century but the fact that it pops up so often on these lists says something about its evergreen status.
I love Ada. Taken together, Lolita, Pale Fire and Ada make up one of the great achievements in 20th century letters. That’s not even counting his two charming pre Lolita Anglophone novels and the two clever post Ada novels.