The quality in a given work of art is not "inherently subjective." I cannot stand it when people mindlessly repeat that bullshit line. Aesthetics, as a science, has existed for over 2,000 years (it was formulated by Aristotle)! You can't go around fucking with the most basic understanding of how things fit together and what people like and then expect people to somehow enjoy themselves with what you've made. Pragmatically, it just doesn't work, plain and simple.
Now, the prequels faults aren't terrible along the lines of anything major, but the sheer number of smaller faults is overwhelming (particularly with regard to the "saga" elements that George thinks he's a genius with). Also, George Lucas seems incapable of capturing accurate portrayals of emotion and that is PARAMOUNT in a story where character drama is a major focus (he had help on this end in the first three films). The prequels are filled to the brim with objective, aesthetic faults and most people expect better results for their hard-earned money.