Only that a poster argued it was the culmination of the film itself, which I find odd.
An argument I disagree with, but I already went over my reasoning for that in the other thread.
Vader's growth and development is pretty interesting, given the way Lucas' drafts went, moving Vader from a separate character to Luke's father to Luke's father in reality. More impressively is the simple way in which it works with Obi-Wan's talk with Luke in ANH.
One of ANH's strengths is (believe it or not) Lucas's writing. All those multiple drafts really helped him par down the script so that for the most part it only conveys the essential information, but also avoid too much specificity where possible, which consequently left a lot of it fairly easy to interpret in any number of ways. It was an agonising process and I'm sure Lucas would sooner walk across hot coals that attempt that again ever, but it did pay off.
Personally I'm a fan of how Vader is characterised in tESB. It seems simple enough on the surface, but if you read between the lines there's a LOT going on there.
A detail people often miss, or mistake for a plot hole is that the Emperor is seemingly the one to tell him about Luke, despite the fact we're explicitly told and shown that Vader is already well aware and very much on the hunt.
Indeed that whole conversation with the Emperor in a brilliant bit of writing because it's actually two conversations happening at once. There's the words they're actually saying to each other, and there's the words they're much more loudly NOT saying to each other. It's verbal chess. Nothing is meant at face value, every sentence has an unspoken meaning. The entire interchange between them is a rosetta stone that tells you all you need to know about their dynamic, and it's the lynchpin of Vader whole arc in the movie.
I know I said the biggest shift in Vader happens between Empire and Jedi, but that's not entirely accurate because the shift actually occurs right at the end of Empire, when he doesn't bother to kill Piett. That's the moment when he just deflated, knowing he'd failed, that his fate was sealed, that he has no way out of this hell he's trapped himself in.
All movie long he's been laser focused on one thing: capturing Luke. He didn't care about the rebels; he scoured the galaxy, mounted a massive ground assault, and committed a fleet of destroyers all to achieve that goal. Nothing else mattered.
The whole time he's murdering his officers left, right, and centre; not because he's angry at them, or because he's being petulant, or petty. It's because they're not people to him, they're parts in a machine. So when said machine isn't doing what it's supposed to, he's just tearing out the faulty parts and jamming in replacements so he can keep going.
So what changed at the end? Why didn't he punish Piett when the Falcon jumped to hyperspace? It's because once it jumped away . . . that was it. No more purpose. I think in that moment he's just so consumed by self pity that he's forgotten Piett is even there. Hell if anything he may even feel like he deserves to have is prize ripped away from him, so complete was his failure. He offered Luke what he thought was "the only way" and he chose to fall to his death. That possibility didn't even occur to him. Who in their right mind chooses death over power?! I think he's so thrown for a loop in that moment that we see the effects of it right up until Endor.
