This is a comment for a rather niche audience, but Barth basically had two literary stages: in his mid to late-twenties, he wrote straightforward modernist fiction (The End of the Road and Floating Opera). The bulk of his career was spent writing post-modern fiction, which included the books most often cited in this thread.

I found his earlier work far more diverting: it featured tight, well-written plots with interesting characters and ideas. By contrast, stuff like Giles Goat-Boy was gobbledygook written for other post-modern academics. Gore Vidal actually has a great essay on this: it seems like Barth started out as a great novelist, but turned toward the (again just my opinion) rather fallow field of post-modernism to further his prestige. Which is a shame, because again, The End of the Road is delightful. I guess my point is this: if your introduction to Barth is seeing people recommend the Sotweed Factor, and you find it inscrutable, I recommend picking up his earlier work instead.