Perhpas the biggest aspect of this espisode is that it deals with bigotry and stereotypes.
"Earth believes the Romulans to be war-like...", says Spock, and all the while the Romulan commander expresses his disgust at war and the loss of his comrades, and questions WHY they must always fight wars.
this was clearly a metaphor for the USSR and it's citizens... and shattered the myth that ALL Soviets were evil war mongers and there were no redeeming characteristics to be found in any of them. Gene expertly remined us that our 'enemies' are also human beings with fears, emotions, regrets, hope, etc...To me this was the greatest aspect of this episode. You felt compassion even pity for the Romulan commander, you wanted him to live at the end..perhaps to become an olive branch..alas not to be...great great episode