Farther than stars said:
Actually, it's not true that those directors didn't add their own vision to those pre-existing works. Making a film is about more than just the plot. You have to factor in so many more elements: pacing, editing, composition, colour pallet, etc. And that's where directors really get to show their creativity. That's what I think Bob meant by the prequels being better than anything Abrams will (probably) make, because "The Phantom Menace" actually excels in all of those areas; it's just that the plot doesn't develop beyond being a backstory for Darth Vader.
P.S. And the acting was bad. There was that too.
P.P.S. With the notable exceptions of Ewan McGregor and Liam Neeson.
You are correct, but you're also right in saying that a film is rarely one person's "singular" vision. A great film is backed up by the vision of many people, from the actors to the editors to the director and screenwriter and musician. The original cut of "The Godfather" was deemed unwatchable until a talented editor salvaged the film through amazing editing. The original 2001: A Space Odyssey tossed out its entire soundtrack in favor of the one audiences now recall as forever linked to the visuals on screen. Little details all collaboratively shape a film's "vision", so no director has "one unique" vision.
But on that same subject, I would argue that the prequel trilogy (let's say The Phantom Menace in particular) is filled with areas where it FAILS to excel in nearly every area. The pacing is incredibly bad, plodding, and meandering. Entire subplots are brought up and dropped. Minor scenes take up massive chunks of screentime. The finale itself alternates between the epic and tragic battle of Darth Maul and the Jedis and the wacky shenanigans of Jar Jar and the giddy cheese of 8-year-old Anakin accidentally blowing up a star ship. The composition of shots is largely lacking due to an over-reliance of CG that prevents proper staging to take place and forces actors to, by and large, just stand around or sit down, or they'll throw in copious amounts of CG that your eye struggles to follow. The CG, itself, is very bad, not in terms of technology, but in terms of violating a very important rule CG artists (like myself) are taught, which is to make a world look "lived in". That means make it dirty. Make it scratched and rusted and grimy and worn and lived in. The original Star Wars is a world that looks lived in and worn in, while the new one has everything pristine and clean and flawless, fresh off the factory floor no matter where they go. It looks fake because the artists didn't take the time to add in the little details that make it look real and believable.
Couple that with bad writing, several bouts of bad acting, a bad story, a lack of any central protagonist whatsoever, and it's a mess of a film that had more wrong than just its director (though he was certainly the one most responsible).
The only thing I can safely say that is "good" about the film without fail is John William's musical score.
