I understand the comparisons to Graham Greene and Evelyn Waugh, but to me St. Aubyn is more like a British version of Jay McInerney, depicting the rich, damaged, and disaffected. There are also some resemblances to John Updike's Rabbit series, and the prose style reminds me of some of my mid-century favorites like Richard Yates and John Cheever.
Never Mind is the story of a single (horrible) day, so it almost reads like a short story. Bad News describes a drug-dependent trip to New York in excruciating detail, and then Some Hope is unexpectedly funny, like a drawing room comedy. Mother's Milk takes place when Patrick has a family of his own, and was shortlisted for the Booker Prize. Surprisingly, these are great when read back to back, and offer a lovely reading experience even though they deal with the toxic effects of family life. And plot aside, you’ll mainly want to read these for the unbelievably good writing.