I think this has to be one of the all-time great moments of DS, and among the most terrifying -- Barnabas rising from his coffin and Abigail getting her comeuppance.
My jaw was agape the first time I saw this scene, and it was again seeing it for the second time (actually the third, or fourth time, since it was re-enacted at the start of the following episode).
Clarice Blackburn did a terrific job with Abigail. She played her within the boundaries of not making her an over-the-top villain, unlike many actors still to come on the series. Her character was believable.
Jonathan Frid matched her in this scene with a performance to make even the stout-hearted quiver and cower. Anger and threatening -- but controlled. (That's the quality so many of the other DS actors were often missing, I think -- keeping the character controlled -- and [shadow=red,left,300]believable[/shadow]).
As I said, one of the greatest scenes of the entire series.