Excellent point. On a tangential note please forgive my Geek, but it was Commander Riker that Kurn talks about having to refrain himself from killing. I would not know this except I just watched the episode (Sins Of The Father) just a couple of days ago.Tony Todd is an excellent choice. Totally forgot about him, maybe because I was trying to stick mostly to regulars. I can remember a lot of lines being given a lot of comedic or dramatic power because of his voice. Particularly when he casually mentions that earlier he had to restrain himself from killing Commander LaForge as Kurn and when he says his last words as the older Jake Sisko in "The Visitor".
Speaking of Klingons, JG Hertzler as Martok and honestly much like someone said about Jeffrey Combs (and I wholeheartedly agree) he is wonderful no matter who he's playing.
Another one that always kind of bugged me was Salome Jens, she just always sounds like she has a cold.
Also the two actresses playing the Duras sisters. I don't think they got on well with the teeth.