Yes, that's the one. I think it's the best of the current series, along with the Kanan comic. I could;t finish the Leia one, boring, and the STAR WARS one is decent and actually runs concurrently with the Vader one, so it's helpful to read both.
I really enjoy the Vader comic. I really enjoyed the book, Rise of Lord Vader, which sucks since it is no longer cannon. I find it really interesting to see the interaction between Vader and Palpatine and what Vader really thinks of him and of his old self.
I may need to check it out too,but here's a thought for you:
Maybe Vader's change was because of Obi-Wan? maybe once Vader figgered out who Luke was Obi started to talk to him? a whisper in the ear at first but later on he actually showed himself,you have to remember (irregardless of how you feel about the prequels) that Obi had one ace up his sleeve and that was he knew how Anakin felt about Padme,so maybe once he got wind of his kids Obi started to work on telling him the whole ugly truth about what happened.
Then at the end something clicked/snapped in Vader's head and he knew the Emperor was why she died and now he was going to kill his son too? and maybe his daughter? I'd think it's amazing he didn't stick the lightsaber up Palpy's backside and twist it.