I don’t find the unpredictability be true, at least in terms of the Star Wars prequels. This implies that the writer considered the implied contours of the prequel story based off of the originals and then intentionally went in a surprising direction. However, most of my issues with the prequels are that they are far too predictable.
Is Yoda the most powerful Jedi in the OT? Better make him the leader of the entire Jedi Order in the prequels. And give him a lightsaber, because Jedi have lightsabers. And make all the Jedi wear desert cloaks all the time, because that’s what Obi-wan wore on Tatooine.
Are the Clone Wars the major threat in the PT? Better make it a single war and make Palpatine be behind it because he’s the villain. And did you think that the clones would be the bad guys? Ha, no they’re actually good! Until they are bad, just as we all assumed, but because of computer chips or some contrived bullshit.
Did Anakin become more monstrous over the course of the films as he gradually lost his humanity to wounds and emotional scars? Oh he lost an arm once, something that is never mentioned again, and then fell in lava and was put in the monster suit twenty minutes later.
Was Boba Fett cool? Uh yeah, cool enough to be the basis for all the clones. And we get to see him as a kid, isn’t that great?!
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And in most cases, the OT implies a far more interesting history than even exists in the prequels.
Was Anakin turned to the dark side because of the evils of the Clone Wars? Nah, he had other issues.
Did Owen know and care about Anakin’s life? Sure doesn’t look like it.
Did Palpatine take power in some Machiavellian plot to trick the Senate? No, they were just dumb as rocks.
Was Obi-wan a reckless crusading idealist in the Jedi Order who flew too close to the sun? Dude doesn’t even have a tan.
Did Anakin speak hopefully of the future life of his child and his wish for him to become a Jedi? Hah, we ain’t got time for that.
Did Owen and Beru begin their lives on a different planet but then move to Tatooine to get away from the Empire? That would have made sense, but no, they’re still hanging out in the same place that Anakin left them, still with the same names.
Was Anakin the best starpilot in the galaxy? No, but he was pretty good at space Nascar as a kid, I’m sure that’s just as interesting.
Where did C-3PO come from? Well I’m glad you never asked but here’s the answer…
…And these are just the character traits referenced in the OT! Imagine what someone could do with an entire trilogy of new events and characters. Instead we get a first movie with the comedic key of Jar Jar Binks and who was practically written out of the sequel, and a second movie with a mystery plot that got written out of its sequel, then a third movie which hinges for its tragedy on clones with previously unknown computer chips in their brains and an entire Senate and Jedi Order whose brains could have really used the processing power.