Romances, huh? Hmmm… (want an extra male critical reviewer, by any chance?)
I haven’t written fiction since I was in my 20s, and haven’t written good fiction since I was in my teens. Being ponderously serious for the most part, I’m a lot better at nonfiction.
But I think that, either way, you just know. The Class A pieces are like gemstones, beautiful from a variety of different angles, independently, and the facets themselves interact to make a beautiful shape. (e.g., the metaphors you’ve been using all work and all revolve around a common chord or theme; the emotional tone of their relationship to the main text, whether semi-cynically making fun of yourself or flirting with the audience with double entendres or making grandiose gestures that echo our culture’s most powerful myths, are consistent, build upon each other, and conclude along with the plot or conclusion; the syntax and formatting and the formality or informality of the footnotes or ‘author’s interruptions’ or little vignettes fit well with the overall tone; etc) The Class B efforts may not have quite that rare feeling of perfection about them, but they succeed in doing what you set out to do in the main theme or plot while maintaining a consistent tone that meshes nicely with the point or plot premise in establishing the reader’s mood, without jarring distractions or elements that don’t play nicely with the others.
Then there are the ones that just don’t quite make it. Maybe they say everything you meant to say and make your points well; or develop the plot and resolve all the unanswered questions and reconcile all the characters’ motivational conflicts by the end of the book, but perhaps there are levels on which it started to work but which stop making sense and sort of fade out unsatisfyingly in mid-stream; or maybe you started out to skewer a perspective and have some nice tongue-in-cheek anecdotes embedded but the overall tone is strident and frantic and fervent, so you end up with humourous little stories ensconced in an otherwise humorless diatribe. Or you’ve reconciled a plot element by having a character suddenly exhibit a new personality that doesn’t fit or contradicts the implicit subtle character development you did before you decided to have the character do this thing to reconcile the plot. Whatever.
In each case, I think that unless you’re a little too close what you are writing about to see past your intentions to see the book, you know if it’s an A or a B or a C, if not when you’ve just finished the last page then at least within a few weeks.