This is about works that, for the most part, never cross the line to bad or good. They just stay roughly in the middle, in the opinion of the viewer. These are the works we often refer to as "decent", "okay", "meh", and "mediocre". Now this doesn't seem important, but some works can still do well even when the audience thinks this about a work. It's a form of comfort food, and often easier to pull off than trying to get the audience to think a work is awesome (which has a higher risk of being horrible if done wrong). Compare Capcom Sequel Stagnation (which often leads to this).