Star Trek goes back to form in examining social rifts caused by people dividing themselves and mistaking symptoms for causes of those same social rifts.
There's a theory that our current social divides stem back to the abundance of viral life forms that infected those living near the equator and warmer watered regions of the planet, and those that lived in more temperate or colder regions were spared the ravages of constant disease. This episode postulates a material cause for the divisions between social groups, notably the white and black populations of post 1950's US, but can be applied to any region of the world where such schisms are manifest.
Towards the end we hear familiar rhetoric of the time, citing the need to resort to civil disorder to address injustices, and the reasons the lower classes must remain in the lower classes; i.e. familiar inaccurate arguments of superior intelligence, lack of ability and so forth. Hence the collision between the two warring factions in the episode. All the while Kirk and crew must address another emergency that is held up by the conflagration.
It's an episode that takes Trek back to form of the first two seasons, though again the production values are somewhat spartan, though still very good. It feels like more money was spent on this episode, but only just. There's still a lack of extras that might have added visual weight, and the upgraded effects of the remastered special edition which are now on bluray, replace the old matte paintings and animation.
What's interesting about this episode is that not only is the script good, but we see another love interest for Spock, only on a more Vulcan (Vulcanian?) intellectual level than the biologically forced pon farr as per the Amok Time episode a couple seasons before. Spock realizes that beauty can stir his otherwise impassive self, but is curious and disappointed when he discovers something about himself.
Another positive is that the plot melds well with the basic story, although there is some plausibility issue with some of the story elements towards the end of the episode.
This is one of those episodes where if there had been a lot more money then it could have been turned into a very decent feature film. Imagine throngs of disgruntled troglodytes, thousands of citizen artists living in Stratos, imagine an escape scene from Stratos with Kirk fighting his way, imagine all kinds of things and you'll get a sense that this is really the good skeleton of a good episode hampered by third season budget cuts.
Give it a shot.