Challenging, funny, deeply thought-provoking. Its just the one of the best things ever. I never tire of reading it and people I tell about it come back and invariably rave about how great it is. I've had quite a few converts to the whole panoply of "speculative fiction" from their exposure to this wonderful little gem.
Brave New World, 1984, Slaughterhouse Five, Gravity's Rainbow, etc. aren't usually what the label conjures up.
"Literature" is the label for works that are good enough that everyone should read them, not just genre fans. "Romance", "Sci fi", "Travel", "Crime", "Comedy", "Detective", "Drama" and so on are works that aren't good enough for everyone to read.
Of course, there's writers who hack their way into the "Literature" section by imitating the quirks of a genuine pieces of literature, or just avoiding all the other categories.
If you move from actually having a subject to making your subject a metaphor for middle-class internal conflicts, you have made the move from Genre to Lit.