I thought they played him exactly right.
To me Vader isn't a rage monster, while he's driven by fear, anger and hatred, he was also very controlled in ANH. The secret of the Sith is that while they are driven by those emotions, they aren't at the core of their being, the core of their being is gaining knowledge through power.
As far as Vader in the duel with Ezra, and Kanan he was pretty much toying with the both of them, when he absent mindedly backhanded Ezra. When he grabbed Kanan's wrist and threw him across the platform, and when he easily deflected the blaster shots back at Sabine he was incredibly casual about it, like kicking a rat.
And remember he wanted them to escape.
I also like how ruthlessly he ordered the burning of Tarkintown.
Yes he dominated the Rebel Fleet and their best squadron.
Remember Kanan's training basically ended when he was still very young, he's untrained, Ashoka is the primary threat and tool to Vader, and you heard the menace when he mentioned Kenobi's name.
At this point, I fully believe that when he faces Ashoka, there will be no conflict, Vader is at the height of his power and fury here, he's still relatively young, and he still burns at the perceived betrayals all around him.
I'm sure that Ashoka will try to talk some sense into him and realize that there is no conflict in Vader right now.
If you go and watch the last season episodes that weren't released, when Anakin is talked to about Ashoka, he reacts to her leaving the Jedi Order with anger and disappointment. He doesn't love her like he loves his son. Given the choice, well he will give her the choice, she will refuse and probably die.
BTW I loved the flat "The Apprentice Lives" and the discussion with the Emperor where they both refer to Anakin as if he's another person.
The season starts in Sept, my PVR is set to record another episode this week with is labeled 203, so I wonder if they will introduce the new inquisitors. We've seen hints of a male and a female, I'm guessing the female is a name from the past
and Dave Filoni has hinted several times that main characters have to die for the story to have impact.