The Modern Library is kind of cheating again. The Way of All Flesh was not written in the 20th Century...it was only PUBLISHED in the 20th Century. It was penned squarely in the 1800s. Samuel Butler had to die first (is this one of the only posthumous publications on the list?) because this book's condemnation of Victorianism, religion, and Butler's own upbringing & family were all too scandalous. Classic Bitch loves her a good iconoclast, and tension like this usually makes for good reading: The Way of All Flesh is no exception!
It's a great read, due in part to its 'first person minor' narration: The narrator is not the main character but is in the story himself and closely (albeit independently) observing and reporting on the protagonist's life. (In fact the narration is so close here that I nearly mistake the protagonist and the narrator for homosexual lovers. Given Samuel Butler's own 1800's-style 'confirmed bachelorhood,' this is apparently not a stretch.) Anyway, first person minor always gives the reader the impression that one is reading the story for a REASON, and there's anticipation of a payoff. Else why recount the life of another if there's no STORY to tell? I suppose what I'm saying is that I trust minor first-person narrators.
Aside from Samuel Butler calling bullshit on a lot of sacred cows, there are a ton of life lessons within these pages as well. To wit: Knowledge comes easily when you're genuinely curious and/or in actual need of information (cf. formal education); stick with results and/or things that can be witnessed concretely or spoken directly (cf. intentions); you are probably better off for the bad things that befall you (i.e., building character). If you liked The Old Wives Tale, Classic Bitch recommends The Way of All Flesh.
A lot of books can be called semiautobiographical, but I think The Way of All Flesh takes the cake. I learn from the book's introduction that some of the letters written to the main character by the main character's parents are reprints of ACTUAL letters written to Samuel Butler by the author's own parents! To the extent that these epistles are cutting, sanctimonious, unjust, what have you, they are mocked within these pages. As it turns out, The Way of All Flesh is rather a good lot of revenge! Classic Bitch is not a very advanced human being, so she finds this tasty reading indeed.