In addition to the excellent answer above:
Brave New World is a comedy. He uses several devices of comedy to achieve this novel of ideas:
situational irony: he presents two extreme worlds in sharp contrast (the utopia of the Brave New World and the dystopia of the Savage Reservation).
satire: the novel is a mix of parody and satire in order to hold up a mirror to human weakness and folly. Huxley creates a "worst case scenario" in order to show the downfall of human
caricature: Huxley uses real people and distorts their beliefs. Henry Ford becomes a god, and Vladimir Lenin becomes a good-looking nurse (Lenina), all as means of showing how pride and folly distorts us all.
verbal irony (hyperbole): Huxley says the opposite of what he means. He exaggerates so as to achieve thoughtful laughter and to make his audience realize the slippery slope in the directions of science and technology as they relate to the death of the individual.
science fiction: Huxley changes time and venue to create a futuristic world state. Little did he know that the dystopias of the Holocaust and World War II were only a few years away, not 400 years in the future.
I guess I would use two words to describe different aspects of the mood that I sense in this book. First, I would say that the society as a whole is surreal. Second I would say that most of the people that we see are desperate. Those two words sum up (for me) the mood of the book.
I think that Huxley makes the mood surreal by focusing on things like the bottling process and like the sex games the little kids are playing. It makes it feel like the society is completely foreign and strange.
When we start really meeting people, the mood is more desperate to me. No one really seems to be getting what they want. Bernard, for example, is not allowed to act in the ways that he wants to. Lenina seems confused about whether she wants to be exclusively connected to Henry even though that is not acceptable to society. By making his characters conflicted and unhappy, Huxley creates a mood of desperation.