Lets be realistic about this... Yes the episode was overly ambitious and there was little chance of a masterpiece but given the restrictions on time, 1/2 hour slot, this episode came out a lot better than it could have.
Since others have summarized the plot I'll be brief. Arthur Takamori, ably played by George Takei, is a Japanese American gardener that shows up at Fenton's, played by Neville Brand, house and is asked to stay for a beer and help Fenton clean the attic. Both of them are haunted by guilt from WWII, Fenton for having killed a Japanese officer and taken his sword after he had surrendered and Arthur whose father had aided the Japanese when they attacked Pearl Harbor. Tensions build and an outside force seems to ratchet things up to the end where Fenton is killed by the sword during a struggle and Arthur commits suicide by jumping from the attic window. Engraved on the sword was a phrase that translated to "the sword shall avenge me". In reality no way but as a plot device OK.
Given the short time from WWII to when this episode was made I can see where the controversy arose. There were a lot of situations where Japanese soldiers had surrendered but were killed because no prisoners were being taken. During some of the island battles there simply was no way to handle prisoners logistically and the soldiers that surrendered weren't trusted. Someone that served with my father in the war had a soldier surrender to him. The Japanese soldier spoke English and had been the in US. The prisoner asked for a cigarette which he was given. They talked while the prisoner smoked it. Afterwards, quite simply, he shot the prisoner. It really haunted him, according to my father, and probably did to the day he died.
On the other side there were a relatively small number of Japanese Americans that either provided information and assistance or entered the Japanese military.
Emotions were still raw on both sides in 1964 and it would have taken a full movie to adequately explore the issues of guilt. Trying to do it in 23 minutes produced a rather shallow attempt. However even given that problem I think that this was one of the more thought provoking episodes and one of the more intense ones. Not my favorite episode but it had real impact.
By the way, the overacting never came close to matching Shatner in Nightmare at 20,000 Feet.