Is an "ingenious plot" enough?
This is the argument made by the critic D.C. Myers. Myers valorizes plot above all else because, in his view, it's a vehicle by which writers convey messages about how and how not to live, or put to the test strategies for doing so. The "greatness," or not, of a writer, then, is for such critics a matter of how well, or poorly, that writer builds a plot, makes it "airtight," and uses it for this purpose. Thus Myers's view, in the cited post, that Wharton's The age of innocence
"...[was]written... to verify a 'tragic view of marital duty'... [with] [t]he verification... accomplished by the plot, which I [can] reduce to a sequence of necessary steps."
Perhaps, but does this make an interesting novel? Life is filled with people, journalism, and lower-grade art telling us how to live, and the number of possible plots is certainly finite, in their broad outlines. Neither advice-column nostrums or an "ingenious plot" strikes me as enough to make anything more than a good romance novel, perhaps with a murder-mystery gloss, the weapon turning up in some unusual place, having been left there by a murderer with an uncommon tragic flaw, the same one the drove her to kill someone a real-life "her" wouldn't trifle with.
Daniel Green takes Myers apart at The reading experience, pointing out that Myers's ideal plot is allegorical - more akin to a debate-class argument than anything else - and thus of little use in most novels. The rest of Green's argument, which he doesn't get around to making, is that a good fiction, novel, story, whatever, should rather seek to capture and convey the texture of the experience of some character or set of characters. Yes, plot, or plots, play a role, and an important one, in making that experience interesting, but that's only a base on which a writer can build. What makes a good fiction deeply interesting, even memorable, is the tension between characters' thoughts, experiences, and their non-thoughts and non-experiences, as well as the tension between those that drive the plot forward, and those that move, or try to move, the characters' lives in ways tangential or entirely separate from the direction of that drive. These tensions, after all, are the sources of the ironies - between life lived, and possible lives, unlived - that give richness to experience.
Moreover, it's not only our own interest in a fiction's nominal theme - the "tragedy of marital duty" or whatever - that should make us interested in it. Playing to this alone, as a novelist, can be effective, but only in the short run - not long enough to sustain our interest all the way through a work, or make it memorable afterward. A novelist, or indeed any fiction writer, to make a work deeply compelling, should raise the questions, "Why do my characters care so much about this thing? Should they?" Then, rather than answer them simply, or encouraging the reader to do so, that writer should structure the work so as to keep them open, and the answers, ultimately, difficult to give, at least without the sort of qualifications that, in life, make even the "simplest" choice, moral or practical, far less than simple. This, again, makes every great fiction, at its heart, ironic. But this sort of irony isn't the cheap irony of a late 80s sitcom, but the sort of irony essential to a rich, examined life, and to both the greatest tragedies, and the greatest comedies.