This planet-based episode with a touch of Greek history explores the idea of "intellectual bullying" with the core message that bigotry is bigotry, whether rooted in intelligence, force, or a mixture of the two.
It's a solid premise (which returns in "The Cloud Minders") that's given an X-Men-like twist where the "superior intelligence" is really just superior ability. Kirk and company, of course, have dealt with this Dunning-Kruger issue quite a few times ("Where No Man Has Gone Before", "Charlie X", "The Squire of Gothos") but the writers have always been careful to protect the regulars from crude humiliation... until now.
Here, we get Kirk slapping himself silly, Spock singing a little ditty, Uhura and Chapel forced to kiss their shipmates, and a dwarf riding Kirk riding like a pony (or maybe some alien animal, considering the peculiar sound Shatner makes).
Put simply, the episode turns into a forum for cheap laughs that damage the characters and the show, with only Alexander the dwarf displaying any depth. (Guest stars Liam Sullivan and Barbara Babcock, likely chosen for their ability to appear arrogant and smirk condescendingly respectively, offer little of interest in their roles as the episode's antagonists).
When all is said and done, the fact that so little of consequence happens is more of a comfort than annoyance, because "Stepchildren" is not an episode worthy of remembrance, though it's sad that it wastes the show's last original score and as well as a fine performance by Michael Dunn (who years earlier was considered briefly for the role of Spock).
Predictably, the episode just sort of came and went in 1968 without much notoriety. Curiously, however, it was retconned by the fans in the late 1970s/early 1980s as an episode theoretically featuring television's first interracial kiss, with fans unaware that Sammy Davis Jr. and Nancy Sinatra shared a kiss on Movin' With Nancy in 1967.
Aside from new shots of the Enterprise in orbit (with the original borrowing the shots from "The Deadly Years" and the new version featuring a highly detailed Earth-like planet instead), the only change of note is a shot of McCoy's tricorder screen which features a more high tech display.