Darth Vader:
-His castle on Mustafar makes sense as it fuels his hatred and anger. I can't quite remember if it was in print or on a YouTube video, but I do recall this being discussed and it makes sense to me. You've lost the love of your life, your best friend and mentor left you to die a horrible death. Nobody is going to be whistling happy tunes after that.
-Having said that, his appearance in Episode 4, to me anyway, doesn't reflect this when he meets Obi Wan on the Death Star.
There's no emotion in his voice, no anger, no hatred & revenge fuelled aggression like we saw when Obi Wan left him to die in ROTS. The best he can manage is a cool
Does that sound like someone who has been holding a mighty grudge for 20 years?I've been waiting for you, Obi Wan. We meet again at last. The circle is now complete, when I left you I was but the learner, now I am the master.
Your powers are weak, old man.
You should not have come back.
While I think that it's great that we saw Darth Vader slice through a squadron of Rebels (the poor schlub on the ceiling gets my vote for the best death in the SW universe) & drop those phat one liners, I really don't think that it adds any extra dimensions to his characterisation in Episode 4.