I used to adore "The Changling" (TOS) as a kid. So much action... a big scary threat is one thing, but there's no way a kid can understand the sexist bits, the scribbled out stuff about a Nomad bolt being more powerful than 90 torpedoes and unique to this week the Enterprise can withstand multiple volleys of those... or the magic behind Scotty being revived on cue. Yeah, Kirk nagging the thing to self-destruct is entertaining but ST: TMP took the same concept of a machine made malevolent by accident after finding a satellite and trying to learn from it (woopsie!) far, far, far better.
"I, Mudd" I used to think was the bees' knees. Now it's just cheese. Mudd was wasted potential, he had more a palpable threat in "Mudd's Women". All the themes are taken too lightly but at least it's cheese with too tight sweatpants and shower curtains. But an episode of throwaway one-liners and moronic eye-candy, what is this - daytime talk TV? Worse, it resorts to Batman-style camp with rubbish like "beads and rattles". Long before the zoom in and out red alert light was featured in LTBYLB (which was an interesting stylistic change that wasn't all that bad...)
"The Trouble with Tribbles" - similarly overrated and forces the comedy a bit much. I don't overtly hate it, but I don't love it as much as I used to. Having said that, it is well written, well structured as a story, and the humor builds up instead of being a hammer-on-the-head-funny every 20 seconds.
"The Way to Eden" I now adore. At least for potential and basic premise and what could have been. Ditto for "Turnabout Intruder", if the writing were more polished. Both episodes have some great acting despite it all. As a kid, both were bland, but "Intrudcer" had the psychological appeal. Get rid of the sexist stuff and focus solely on Dr Lester's insanity and the episode wouldn't be so reviled. Yes, 1969, Roddenberry allegedly wrote it to attack any number of vectors, but it didn't quite work.
And "Eden" was shown well past its topical sell-by date. Now if we had today's youth trying to be hippies, the story might work better. Or even a rewrite would make it an allegory on whatever disease of the week strikes one's fancy, based on Dr Sevrin's character.
"Plato's Stepchildren" is a high concept horror show, with one of Trek's all time best interchanges - between Kirk and Alexander. Also loved it because it's creepy as hell. Though keep in mind the UK did an interracial kiss years before the US, and without using coerced sexual assault from the Platonians onto Kirk and Uhura as a plot device. People love quoting the scene but have they actually watched the thing?! /rhetoricalquestiongiventheobviousonlyanswer
"City on the Edge of Forever" is good but an overrated misfire, possibly due to script rewrites that Harlan had no control over. The premise is there. Given the context of the 1960s and TV censorship, it's earned some just due accolades on its own. But at the same time, 1967 or not, had the episode really hit it home that a pacifist had to die in order to prevent Hitler from winning... but she's just splattered in some, as they say, rando crash. They had no guts, pardon the pun, to really dig into the temporal deviance and intellectual paradox.
"Who Mourns for Adonis" - never liked it as a young kid as nothing really happened and a big hand in space... meh. As an adult, I appreciate more the special effects (especially with picnic table placement for Apollo growing and yet Lt Palamas wasn't trying to look up), there's some lovely eye candy for all, and for once the writers are getting beyond "the big three" by having Spock cite Uhura's importance. It's still not much of an episode, but those little set pieces - and the show was deemed made for adults back in the day, not kids - elevate and add much more than what I would have fathomed as a kid. Still, season one by far has the most bits and set pieces for anyone who's not the big three.
"Gamesters of Triskeleon" - mediocre as a kid - "Oh look, they're fighting but those glowing collars are cool so why isn't KMart selling them". And I laughed at other shows using either the token stock fight music, and/or Triskeleon logo, as an in-joke in the way audiences are supposed to. As an adult, apart from too many unnecessary jokes involving Jiffy Time stove top Popcorn, what makes me love the episode - apart from some nuanced scenes (Margaret Armen was a fantastic addition to the writers' team) - the discussion of slavery (thralls) does hold enough weight. Though if Kirk would beam up Alexander, why not do so for Shahna? Kirk had to side with his ship but he did genuinely love her, which is a rare side of Kirk as usually he's wham-bam-then-warp-eight-how-great. Missed opportunity, but it's the only real misfire in the episode.