APPOINTMENT IN SAMARRA is O'Hara's first novel and often considered his best. It is a concise (251 pages) and somewhat terrifying tale of hubris in the modern world. Set in 1930, it is the tale of Julian English who, at the novel's start, resides at the top of Gibbsville, PA's social structure, but who loses everything in a breathtakingly short time. English's struggle to retain his social status and everything that goes with it is tense and has a certain classical element to it. When the editorial board of the Modern Library (Random House) published their 100 Best Novels of the Century, they put Appointment in Samarra at number 22.
If you're looking for a good old-fashioned long novel that takes weeks to get through, you might want to try O'Hara's FROM THE TERRACE and RAGE TO LIVE. The library has new paperback editions of all three.