Two campy episodes in a row! Thank god they weren't aired in this order.
This episode bears the same exact story as Charlie X: an alien with a toddler mentality has great power which he uses to torment the crew of the Enterprise, before being chastised by the fortunate appearance of his ethereal parents. The central alien this time around, rather than being an angsty teen, is a foppish man who has been studying medieval earth.
While Charlie X may be the superior execution of the concept, I cannot deny the charm of this episode. The alien the crew falls victim to, Trelane, is fantastically interesting with the lethal games he subjects them to.
We begin with the disappearance of Captain Kirk and Sulu from the bridge. They follow the mysterious whodunit down to the planet's surface, where they encounter their host: the harpsichord-playing dandy, ex-General (now Squire) Trelane. His castle dwelling houses a perfect visual indication of the character's flagrant conceit: a large mirror, which reveals itself to be the mechanical source of his power.
This is, however, a footnote subservient to the great flamboyance of Trelane, which is the true iconography of his character. He dances with the women, makes racially questionable comments to Uhura, and challenges Kirk to a duel. Strike that, multiple duels.
The madness rises to a crescendo as Trelane chases the Enterprise with his entire planet of Gothos. Yes, you read that correctly. He chases them with a planet. I'm not sure there's much more I can say, after that.
Like Shore Leave, it is a great bit of fun without any thematic or conceptual ambition. Others have postulated this episode to be a meditation on power, reflected in Kirk's reaction to Trelane. I do, however, find this analysis unfounded, and almost entirely unsupported by the content of this episode. I also generally find the choice to invoke the word "meditation", or its equivalent, to be a precursor to a loose interpretation that reads more into the work than can be supported.
There are a great many playful turns of phrase in the dialogue that echo the lofty character of Oscar Wilde. This mentality is opposed by Spock, who retorts, "I object to you. I object to intellect without discipline. I object to power without constructive purpose." This is more telling of Spock's character than it is of any authorial depiction of theme.
This episode is, as Trelane would say, "Absolutely smashing!"