I don't really know how to sum up this episode. It has some good bits, and some not so good bits.
With Mr. Spock being badly wounded in the teaser, it is nice to have a Kirk-McCoy combination for the bulk of the episode. I like Spock, but it makes a change from his logic-driven manner driving the story for once.
Some don't like the Mugato. Indeed, it is quite obviously a man dressed in a giant white suit with horns on, but at the same time, I personally quite like it when the series goes for such alien beings. I think it was just a result of the limitations and budget of the era that prevented it from looking any better.
The Klingon of the episode is very good, and probably one of the best Klingons seen in the Original Series; He comes across as very cunning and sly.
The first half of the episode is by far the better, with a decent story. Later, after Kirk is healed and indebted to Nona, things start to lose their way slightly.
Kirk's decision to arm both sides equally is very questionable, but at the same time believable, as there seems to be little logical answer to the situation.
The ending of the episode is very good, with Kirk not sure he has made the right decision.
As I say, I'm really undecided how to sum this one up; it has some good bits and some weaker bits. In the end they even out and end up as a mostly average instalment.