Ray Davis (Pseudopodium) suggests that, while such books as Nabokov's Pale Fire and Cortazar's Hopscotch can be appropriately labeled "experimental" fictions, the fiction of John Barth is instead only a "generic" member of a category that has come to be identified as "experimental fiction." Barth's work, presumably, simply makes a number of familiar moves that have been accepted as "experimental" in this generic sense.
I would agree that such a category exists, and that those writers who could be consigned to it do indeed mostly reprise certain recognizable techniques or repeat what have become by now fairly well-worn tropes. But I can't see how Barth belongs to this category. Many if not most of the techniques in question (techniques of self-reflexivity, self-reflexively applied) were actually introduced by Barth in the first place, and the idea that conventional fiction had become "exhausted" in its ability to keep serious fiction afloat--and that a new kind of fiction able to confront this fact head-on was needed--was Barth's idea.
Certainly Barth had his own precursors. In "The Literature of Exhaustion," he cites Nabokov, Borges, and Beckett as the kind of technically adventurous writers whose company he would like to join, and, even further, praises Borges for his recogniton that no writer is truly original--such a writer would be unreadable, would make it so difficult for us to find our literary footing that the effort wouldn't finally be worth the trouble--but in effect is merely commenting on what's already been done. ("Pierre Menard," for example.) Thus Barth acknowledges that all literary writing is, in this broadest sense, generic writing. Moreover, Barth also confesses that he himself is a writer who "chooses to rebel along traditional lines," perhaps only inviting the charge that he's really not very innovative after all, merely imitative of his own favorite innovators--who themselves aren't really innovative, either, etc., etc.
But I really don't see how anyone could read Barth's early work, from The Floating Opera to, say Chimera, and conclude that Barth is not engaged in a fairly earnest kind of literary experimentation. If any of these books seem deriviative at all, they would be the first two, The Floating Opera and End of the Road, which are not only fairly conventional narratives (with a few modernist flourishes) but also embody "existentialist" themes of a kind rather popular in the 1950s/early 1960s. On the other hand, The Sot-Weed Factor clearly shows Barth looking for inspiration elsewhere than modernism, specifically 18th century picaresque narratives. The picaresque had not been entirely abandoned, of course (The Grapes of Wrath), but I think Barth can genuinely be credited with refocusing attention on the picaresque specifically as an alternative to both modernist introspection and the well-crafted realistic story. This may not be sui generis experimentation, but it seems to me that in the context of the time it is undeniably a literary experiment.
Giles Goat-Boy is an even more thoroughgoing effort to reconfigure the mid-century American novel, and to explore more fully the potential of "archetypes" (a la Borges) and of what Robert Scholes called "fabulation." . Although I myself find it less compelling than The Sot-Weed Factor (it's an example of the "art of excess" that's finally just too excessive), again I find it hard to believe that many readers could attempt this novel without finding it quite a singular work of fiction, at least within the context of postwar American literature. Forty years later it can try one's patience, but this is because Barth was trying to do too much, not because he was just working over a formula inherited from his literary forebearers.
But it is Lost in the Funhouse in which Barth most purposefully engages in literary experiment. So singlemindedly does he do so, in fact, that readers who encounter this book now, shorn of the context in which it was both so controversial and so influential, might think it dated, a relic of an era in which experiment in fiction could be so noteworthy. (They would be mistaken to judge it so, however, as it is an example of the sort of fiction that, in Barth's own words, is still "au courant" but also "manage[s] nonetheless to speak eloquently and memorably to our human hearts and conditions, as the greatest artists have always done.") Here readers will find: a story in the form of a cutout Mobius strip; a story narrated by a spermatazoon on its journey of fertilization; a story in which the narrator (the author's recorded voice) pleads with the author himself (standing by) to put it out of its misery; a story narrating its own coming-into-being; a story about speaking in tongues in which each of six brief speeches is "metrically identical" to the Lord's Prayer; a story that takes the notion of story-within-story to its hilarious limits; and stories such as "Life-Story" and "Lost in the Funhouse" itself, perhaps the prototypical and most influential metafictions in postmodern American literature.
Again, perhaps reading such stories after close to forty years of "experimental" fiction by other writers coming to terms with the implications for the future of fiction these very stories themselves brought into the open makes it easier to see how their innovations are to some extent coterminous with the practices of other forward-looking writers throughout literary history, might even by this point seem overused. But that in 1968 Lost in the Funhouse was unlike anything else being done by Barth's contemporaries (with perhaps the exception of his like-minded colleague Robert Coover) seems to me indisputable.
Barth is perhaps legitmately vulnerable in his later work to the charge of repeating himself, of abandoning the kind of focused experimentation to be found in Lost in the Funhouse in favor of a more lighthearted self-reflexivity drawing on Barth's own life and probably more interested in depicting his native Chesapeake Bay region than in advancing the cause of innovative fiction. Books like Letters, The Tidewater Tales, and The Last Voyage of Somebody the Sailor have their pleasures (I find the latter to be a particularly affecting novel), but certainly Barth's reputation as an important American writer could not really rest on them, however much they add to a critical consideration of Barth's work as a whole. And I do believe Barth will ultimately be judged an important postwar writer, largely because of the accomplishment of a book like Lost in the Funhouse, which, however much it absorbs the influence of writers such as Borges and Nabokov, also transforms that influence into a frequently outrageous kind of comic fiction that discloses the many ways in which storyelling can trip over its own narrative feet, but in the process demonstrates that fiction still has plenty of innate if unexploited resources from which it might continue to draw.