CWBorne said:
You can find all sorts of quirks with Vader in a ANH in contrast with ESB. He seems much more emotional in the former, and while ruthless doesn't seem like he would kill his own officers at the drop of hat. (In fact given that Vader only kills officers via force choke in ESB, you could easily imagine that he's just really desperate to find Luke and typically wasn't like that through out his entire run in the Empire).
This ties in perfectly (and actually helps make my point) of Vader as a Captain Ahab type character in ESB, going mad on his quest to find something that will ultimately destroy him.