Worst episode ever? Hard to say for sure, but this would certainly be a nominee. The real problem here is that Bixby has tried to adapt a stand-alone idea into a Trek episode. It not only doesn't work, but it flames out memorably.
The script is so bad that it is not even worth discussing. Our characters simply aren't our characters. The guest has his own elaborate and very interesting backstory, but it's told clumsily and hastily, and most of what is interesting about it is bypassed in favor of the android story. The android is interesting, but the Shakespearian overtones in her death (dramatically recited by Spock) are far too grandiose for the context. Shakespeare this ain't, and attempting to channel the Bard just rubs salt in the wounds created by the very bad storytelling.
Of course, there are some notable successes and failures. The M-4 looks like the love-child of Nomad and a collander. And couldn't they have figured out a way to make it move without swinging like a bad swag lamp? Flint appears to live on Rigel VII, and wears the shortest skirt in the episode (paisley, no less -- complete with cape!). Shatner's acting rises to new levels of parody-inducement. McCoy seems fond of stating what everyone has already figured out (that third season condescension again). Spock seems to have all the answers, and actually knows how to play the piano! Embarrasing, that's what it is.
What Spock plays, however, is one of the episode's few successes: a Brahms paraphrase created by Ivan Ditmars (better known for his work on "Let's Make a Deal"). It is lovely and most plausible, and gets heard in its entirety. The other success, as you may have guessed already, is the fabulous gown worn by Rayna. As is true so often with these costumes, their success is dependent partly on the fabric and partly the engineering. This one is beautiful without being too mystifying, although it genuinely feels out of place in its setting.
One must also credit Sorel for creating a character who is plausible as an android right from the start. Unfortunately, she's so plausible that she almost gives away the episode's secret in her first scene. Daly doesn't fare so well, managing to look wooden from just about every angle (except when his stunt double takes over).
But the only lasting success in this episode is in the very last word of dialogue. In a scene which is excruciating for so many reasons (Kirk pining away for a dead android, then falling asleep on his hands, not waking even though two people are standing over him having a conversation, and then McCoy cruelly turning the knife in Spock's Vulcan heart), the final moment is one of the most tender things Spock would ever do for his captain. That simple act is enough to remind us of what this series has been, and could have been.
Rating: Very Bottom (7)