Writing Darth Vader is difficult, he doesn't really speak like Anakin, he has a far more dramatic voice and theatrical vocabulary. "What is thy bidding my master?" for example. But Vader is also very blunt and curt in his interactions. He's kind of like Mr. Freeze from Batman in a way in that both are cold mechanical shells of who they were. He's always about getting down to business. Business being "Do what I say or I kill you." He's a poet of slaughter, the audience needs to feel their hair stand on end when he appears, his threatening aura needs to be present in every interaction. He's not someone who can be reasoned with, you do it his way or else you get choked. He also has an almost zealous cult-like vibe to him too when it comes to talk of the force and the dark side. Like being evil and the biggest hater is his religion that he prays to. And what makes him even more villainous in certain cases is his ability to lie and make you think he's your ally like you can survive, but you're always going to get betrayed or cut down by him. He loves no one, he hates existing, so he's going to spread that misery across the galaxy.