The biggest problem with the Prequels is a poorly conceived story arc followed by atrocious writing. Other than both Lloyd and Christensen and Anakin, the cast was pretty solid. Sure they were CGI heavy, but most of it still holds up. The art direction and design are probably the strongest points and they are gorgeous, although in many respects they don't match the look of the OT. Essentially the prequels are pretty to look at but lacking of any soul. They were probably doomed from the start because Lucas had close to zero passion for the project. I remember watching some of the featurettes, and he just seemed to be going through the motions. Whenever he was directing a scene he's leaning back and lounging in his chair. Of if he was picking out a design or making a creative decision, he's browsing through choices like he's in a department store. Whereas if you watch the OT featurettes he's always leaning forward, engaged and 100 percent into it. There was an urgency and even though the budgets got bigger, there was always a bit of an indy edge to it. It has less to do with age. There are plenty of directors in their 50s, 60s, and 70s who direct with passion and zeal. The studio didn't care, they just wanted to make money. I still think there is a single epic 2-hour movie that could be made by re-editing, remastering, and some reshooting. Given all of the special editions that have been done with Lucas's endless tinkering, why shouldn't Disney hire a hot shot director, give him $50M to produce the ultimate edition prequel movie that gets rid of pod racing, midichloreans, Trade blockades, JarJar and the gungans, talking battle droids, and all the other nonsense, and instead tells the story of a promising and powerful young Jedi who lost his way, turned to the dark side, and helped a tyrannical Sith Lord enslave the Galaxy. Desaturate and weather the color palette, remaster some of the CGI designs, redub the dialogue and that alone would give it some edge.
Spoiler:
