What I've always admired in him as an actor is the degree of physical control he has, but not in a way that comes across as stiff or unnatural. We know in the end that he's BS'ing, but the way he says, "Goodbye, Nerys..." Whoa.
I ended up using a frame from "Covenant" as a pose reference for a drawing I did of my alternate-universe Dukat (who is Dukat's "good twin"). I changed the expression to fit my AU Dukat's personality.
Here's the drawing:
(Please read the description...it'll explain why, in that drawing, AU Dukat is so sad.)
It took a few changes to turn him from "fake-subdued," which you see in "Covenant," to the truly reserved individual he is in the AU, who tends to take things to heart, but I don't think the drawing (of him, anyway...I messed up on the human) would've come off without the great job Marc Alaimo did in that episode:
(It's funny...while Gul Dukat is still, I keep picturing AU Dukat, in that drawing, fidgeting with his hands.)