This episode tends to be one of the "average" third season episode in that most despised of seasons. The idea of some indestructible woman running around causing every cell in your body to rupture (ouch!), who is intimately familiar with you, and can appear anytime and anywhere, is suitably creepy. Lee Meriwether actually has the acting chops to handle the role of a computer programmed with the conscience of its Commander. Although the Kalandrans (who we'll never hear of again) sound like a pretty nasty bunch. Losira too, since she programmed the outpost computer to kill anybody who wasn't a Kalandran. She was compassionate enough for her duplicate to hesitate in killing... but not to program the thing to brutally kill people in the first place. Okay...
You'd think there'd be a more efficient way to kill intruders, though. Like "Spectre of the Gun," aliens need to come up with quicker ways to kill the outsiders.
The secondary crewmen are actually mildly interesting here, which is rare in the third season. D'Amato is played by 60s stalwart Arthur Batanides, and his line about not being frightened of geological phenomena is kind of amusing. The doomed Watkins actually gets a moment to try and bluff the Losira program: wish he'd succeeded. And Rahda (the show's first vaguely Indian crewmember) gets to be the one to figure out what really happened to the planet (even if it's kind of "duh"). Dr. M'Benga doesn't make much of his second appearance on the show but at least he gets to do something.
Sulu gets short shrift: Kirk gives him a hard time at least twice: comparing him to Chekov, Ouch! again.
Kirk and McCoy don't have much to do (and McCoy seems rather facetious). But watching Leonard Nimoy and James Doohan bounce off each other is pretty funny. Spock doesn't seem to have learned much from his failed captaincy in "The Galileo Seven." He gives Rahda a hard time for not knowing the precise time, and seems more concerned with his head then where what happened to the Enterprise.
Both climaxes are pretty climactic: Doohan milks the drama and last-minute save for all its worth, and its glad to see 23rd century tools still jam. Although this part doesn't make sense: okay, what's jettisoning the access tube going to do? If it's going to stop the ship's destruction, then why don't they just do it and not send Scotty in, in the first place? If it isn't, what difference does it make whether they jettison Scotty or not. And yes, the Enterprise gets to exceed its top speed yet again.
The climax on the planet is equally creepy although more because of the implied threat of a painful death. The landing party seems reluctant to actually _touch_ the Losiras. And there's a kind of "Well, we're going to starve anyway, so let's go into the Cave O'Doom and... die?"
Still, I generally give this a high rating based on Meriwether's performance, the generally creepy ambiance, the secondary crew getting a chance to shine this late in the game. It's enough to overcome the plotholes.