It's not a big deal to modern audiences of course but one thing that struck me about the episode was how the commodore of the starbase who also happened to outrank Kirk and put Kirk in his place several times during the episode was played by an African-American actor. I can imagine when tv audiences first saw that episode in 1967 that there was some controversy aroused.
Not as much as the kissing scene between Uhura and Kirk in the south. IIRC several stations refused to air that episode.
