
But watching it with her repeatedly has made me realize something that had never occurred to me before.
Darth Vader is a moron.
Nearly every decision Vader makes in the movie is wrong. He captures Princess Leia's ship, yet inexplicably allows her to transfer the stolen data tapes (his whole reason for attacking) to the surface in an escape pod. He wastes precious time having his thugs stage a fake Tusken raider attack on a Sandcrawler, and destroy Uncle Owen's farm, when recovery of the missing droids ought to have been a gilt-plated priority.
Vader then allows the Millennium Falcon to escape Tatooine, even though he's already been informed that it's the vehicle carrying Kenobi and the droids.
On the Death Star, he gets into a silly argument with one of Tarkin's officers about religion, choking the guy with his hocus-pocus mind control trick for no particular reason (we'll see Vader's management style in action later in The Empire Strikes Back, as he kills one highly-trained general officer after another, ironically because he believes them to be incompetent).
Vader then allows the Millennium Falcon to escape a second time, this time deliberately, betting that it will lead the Empire to the rebel base before the rebels can find a weakness in the Death Star's defenses. Again, he guesses wrong.
He kills Ben Kenobi, but immediately loses the body.
When the Death Star is attacked by X-wing fighters, he leads a group of fighter pilots against them in ship-to-ship combat. The obvious solution to the problem -- turn the tractor beam back on -- never occurs to him. Vader's Tie Fighter defense fails. As a result, the Death Star is destroyed, billions of Galactic credits go up in smoke, thousands of Imperial soldiers are killed, and the only guy who comes out of it with all his skin is Darth Vader. Figures, doesn't it?
Had the guy been even remotely competent, he would simply have blown Leia's ship to pieces before it reached Tatooine's orbit. She would have found it difficult to transfer the stolen data tapes to anyone while floating in vacuum amidst the twisted wreckage of her blasted ship.