Currently re-reading, May 2012! 
 ... 
 Old review: 
 In 1974, the three-member Pulitzer Prize jury on fiction supported Gravity's Rainbow for the Pulitzer Prize for Fiction. However, the other eleven members of the board overturned this decision, branding the book "unreadable, turgid, overwritten and obscene". 
 A brilliant mess of a novel, as perhaps suggested by the wikipedia quote above, Gravity's Rainbow saw Pynchon pushing his convoluted narrative tools as far as they'd go. The book seems to be about the fetishization of death by nations at war, and about the cold-war ICBM horrors latent in World War II's German V2 rockets (whose trajectories lend the novel its title), but it would be diminishing to try to reduce the book into any set of well-defined terms. 
 I'm not sure it's actually Pynchon's best book, having more enjoyed the somewhat more approachable V and Against the Day, but it certainly seems to be his most ambitiously styled and densest-woven, and certainly earns and rewards the study it receives. And perhaps, returning now that I've read those other books, I'd find it to be a little less aggressively scattered. 
 Also of interest: Zak Smith's Illustrations for Each Page of Gravity's Rainbow.