A shocking account of a young black widow who seduces and destroys a kindly elderly gentleman, this book offended me because having sex with old dudes is gross. Ask my wife! Ba doom crash. Wait, you say it's about what now? Oh. Well, whatever.
Anyway: show up for the icky sex, stick around for the language. The plot honestly drags a little at times, but Nabokov's writing is about as beautiful as writing gets.
Update, December 2012: I read this again. The weird thing about Lolita is that it's easier to admire than it is to like.
I've rarely seen an author as in control of what he's doing as Nabokov is. He has the whole thing mapped out. The way he teases you with lasciviousness in the first third, and then pulls the rug out from under you, showing how mundane and gross the reality of Humbert's relationship with Lolita...extraordinarily well done. And the way Clare Quilty is teased out: again, masterful. This is one of the trickiest murder mysteries ever written.
But I feel like there's a perverse refusal, among critics, to acknowledge that this book drags in its second third. It just....it gets boring, man. And it doesn't even fully recover in its final third. The first bit is the best. As writing, it's rarely matched; but as a novel, it's only pretty good.