#19: Charlie X
In case you forgot: Emotionally stunted teen with godlike superpowers terrorizes the Enterprise until his adoptive, immaterial parents take him home.
Charlie's awkward early encounters with other people are charming; there is a ring of naive authenticity in the ways he goofs up. There is the same kind of authenticity in the punishments he doles out during his temper tantrum, in that they seem like the kind of thing a distraught and totally alienated teenager would think of. The woman with no face in particular is some freaky stuff (and is a Google suggestion when you image search for Charlie X, so I guess that brief scene really made an impression). The few moments of Spock being forced to recite poetry manage to be both kind of funny and kind of terrifying at the same time.
What makes the episode stand out, though, is the end. Charlie's fate—to return to immaterial beings he can't touch or love—is pretty grim. Kirk's pleas with the aliens to allow Charlie the chance to be rehabilitated so he can be with his own kind may be one of the highest points for Kirk's character: even though this near-omnipotent brat just destroyed the Antares and took over the Enterprise, Kirk still has enough compassion that he can't doom Charlie to such a future. But the aliens are right, and Kirk and the crew and the audience knows it. Charlie is probably beyond rehabilitation, or at least beyond safe rehabilitation. A lifetime of solitary confinement is his only option—that or death.
The fact that the problem resolves itself despite (and without) any efforts of the Enterprise crew makes the ending, dramatic and disturbing as it is, a little bit unsatisfying, even if this isn't the only time it's happened. At least that interference makes for a nice irony to the episode: the very powers that condemn Charlie to his terrible future were originally given to him to save his life.
While Charlie's initial butt-slap of Yeoman Rand is funny—it's such an obvious mimicry of what he witnessed between two crewmen that you can't really blame him for thinking it would be okay—the way no one involved can talk about personal space, bodily integrity, and respect is just frustrating. Some humor doesn't age well, and this particular humor drags on for far too long.