I think that multi-dimensionality is what makes Dukat stand out amongst all Star Trek antagonists.
He was capable of what could be considered pure evil by others (but they were still acts he could rationalise himself as a true Cardassian working to keep her strong). He could try and be fair (with the Bajorans as he understood fair i.e the story related in Waltz, but then take cruel action when they acted against him). And he could also love his daughter without reserve, and lose his mind when he lost her.
Dukat is by far the greatest Star Trek TV antagonist ever created.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist