What sort of mood does Huxley try to create in this book? How does he accomplish this?

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.