Uninspired, unoriginal, and cliche. Overuse of the same washed out formula. Death by exposition. Authors unrepentant cheating by using asterisks, flavortext and other lazy methods. Character progression too much, too soon. Bad characterization with implausible decisions and no context nor explanation. Pacing in general is terrible. Exceptionally poor authorship. Even if it's hot on the front page, doesn't mean it's good. When the plot has just one big plot hole or several more to the point of raising more than one red flag-it's a dealbreaker.
Stories that aren't outright crap and fall short of par for various reasons. Aside from objective quality, disappointment is often felt instead of spite. It's a shame to see potentially good stories flop. Even more disappointing when there's that one, two or few holes in the plot or character(s) that de-rail the story into being unfeasible. All it takes is one red flag and dropped like a turd.