When At Swim-Two-Birds was published in 1939, James Joyce was encouraging, calling the young author "a real writer, with the true comic spirit" (a spirit in short supply in the war-birthing world of 1939), but Dylan Thomas won the battle of the blurbs when he said of this novel, "This is just the book to give your sister if she's a loud, dirty, boozy girl." Decades later, Anthony Burgess called it a "funny, vital, shocking" masterpiece, Updike wrote of it admiringly, and even John (no relation) Wain climbed down from his horse, shot bad Jack Elam right between the eyes, and drawled that O'Brien's novel was "just about the only real masterpiece in English that is far too little read and discussed."
Having just finished the book, I find myself in only partial agreement with these distinguished blurbers. At Swim-Two-Birds is indeed a good, funny book; it's engagingly written, formally original and playfully experimental, a highly amusing and even more highly literary entertainment--and most importantly, it's not green. (One of O'Brien's Irish eccentrics considers all books bound in non-green covers to be a priori heretical, a surprisingly complex authorial swipe at both Irishist kitsch and the banning of Ulysses in its original more-blue-than-blue-green Shakespeare & Co. wrapper.) A good case could be made for ASTB as the first truly postmodern novel; it's so proto-pomo that it often reads more like a descendant of Barth, Barthelme and Vonnegut than one of their precursors. (Or as an old American novelty song once put it, "I'm my own grandpa...") It's at least 30 years ahead of its time. But, alas (hear the gears clunk as I shift from laudatory to critical mode), it's also quite uneven and ill-paced; it sags in the middle, some scenes go on too long with too little humor, like those tedious Saturday Night Live sketches that don't make it into the edited one-hour reruns. O'Brien probably couldn't have written a more original novel, but he could've done a funnier one. The book also has a major 'anxiety of influence' problem: the lengthy pastiche scenes (the book's most tedious sections, to me) pale before their obvious precursors in the 'Cyclops' episode of Ulysses; and the most often remarked-upon aspect of the novel, the trial scene in the final third, is too close for comfort to Joyce's 'Circe' episode. So I wouldn't call At Swim-Two-Birds a masterpiece; it's more of a minor but very amusing tour de force, the impressive early work of a Joyce-smitten young man.