Both characters were well written and well played. I see from the IMDb that Colicos played Kor in spin-offs, but I have not seen those episodes. (Nor Kang's later appearances.) He played the first of perennial "bad guys" in TOS. The scene where Kirk tells Kor to "go climb a tree" is a favorite.
While I would have loved to see Kor and Kirk knocking heads again, Campbell (as Koloth) and Ansara (as Kang) kept TOS from feeling too "small." All are fine actors, but I must remark on Ansara's "exotic" features. Acting aside, Ansara's face gives him presence in any role.
Kor seemed less overtly threatening (he'd smile while threatening to suck your brain dry), yet dangerously clever, too, and not to be underestimated. Kang looked
dangerous. Since Kirk can grip a blade by the sharp edges and not get cut, I will let him shoulder roll with these two. I'm happy to sit back with some popcorn and enjoy the show.