Bingowings said:

I know Michael Pennington can act but he is comically awful in ROTJ (he looked like he was going to pee his pants all the time Vader was onscreen).

That's not awful, that was exactly what he had to act. The whole purpose of Vader's arrival was to "put him back on schedule" and Vader had a particular reputation by that time. The point of the first scene is to establish Emperor's reputation through Vader's reputation. Pennington did a great job in that scene. He acted a bit unconcerned when only Vader was in the picture, but when Vader mentioned Emperor he did almost pee himself.