An example of filling in a detail that would make that universe *cooler,* by the way, is to show that the Emperor tried to use the same trick twice: the first “rebellion” that gave him power was of his own manufacture, why not make the rebellion that gave him political position to dissolve the Senate entirely *also* his? But oops. This time it worked too well.

But I digress. I think you left out the inescapable tautology of drama — the thing that makes a cool villain cool is his or her coolness. Vader was cool because he had cool armor, and a cool voice, and a cool (literally dispassionate, which is weird lore-wise but whatever) attitude.

And yes, that was a huge factor in what made him a good villain — his coolness made him memorable. Which is sort of requirement zero. You can’t have a good, forgettable villain.

But I have to disagree with you on another point you make: Vader was a good villain because he was in control of his situation. In the structure of the movie, Vader was pretty much on top of things. He knew where the princess was, he knew she had the thing, he knew how she was getting rid of it, he organized his soldiers to find it, he made sure she stayed alive long enough to be “rescued,” he used his most inept soldiers to “foil” them, he killed the only one he actually cared about killing, he tracked the princess to her base, and he disobeyed orders from his stupid boss to go deal with the single actual threat they posed.

He knew his shit. And while he did let Tarkin stop him from killing the lt. mook, he made the point he actually wanted to make — roughly, “Maybe religion doesn’t make a difference to everyone, but it sure does affect your life!”

Now you could argue that Tarkin was really the strategy and Vader was just the muscle in all of that stuff, but that’s not really how it’s portrayed in the movie — Vader’s always got the center-stage, and while we get plenty of opportunities to see Tarkin being an idiot, we really only have allusions to Vader at worst taking it slow in his pursuit to personally choke to death every single person in the galaxy. (We even know Tarkin’s not his real boss, because the princess acknowledges Vader before she does Tarkin.)

Ben and Leia are intelligent, resourceful leaders; Luke is a kid with magic space powers; R2-D2 has the tech edge; Han has a special spaceship; Chewie’s a powerhouse. Vader has all of those things — in one character, all the strengths of the heroic group plus the backing of a giant faceless empire. If it wasn’t for the Power of Friendship, he would have won (and presumably stopped the laser at the last second, said, “Yo, I got this,” and gone down in his special spaceship and personally force-choked the entire Rebellion to death one dude at a time).

tl;dr. i know. it’s okay here’s the summary:

…and THAT is what makes him a good villain. He engages the heroes on their level (and does it in a cool, memorable way). All of the best villains are basically just the hero (or hero group) dressed in black (metaphorically, but also usually not), minus moral superiority and/or the power of friendship.