Kor, Koloth and Kang pretty much acted the same and probably could have been played by the same actor
It goes deeper than that. Koloth exists because they couldn't get John Colicos back to play Kor. Kang exists because they couldn't get John Colicos or William Campbell back to reprise Kor or Koloth. Each was initially conceived to be the one before, and was changed because the actors were busy with other roles.
I like it. It gave us three compelling characters, each with his own quirks and individual traits. My only disappointment is that the only time the three of them worked together as Klingons, two of the characters died, preventing it from happening again. I enjoyed their interplay very much.