We all have episodes we don't care for. Episodes that just let us down to some degree or other. It's been said often that TOS could be bad, but never boring.
I certainly have my choices of episodes that let me down, but even in those dim moments I've usually been able to find something that I still liked...if only there could have been more of it.
At any rate why don't we take a shot at citing something we liked in episodes we were otherwise disappointed with?
“The Apple” - Yeoman Martha Landon kicking ass. Seriously the entire series could have used a bit more of the female contingent of the Enterprise crew mixing it up.
“Spock’s Brain” - There are some genuinely dark and chilling moments in this episode, but they're mostly in the early part of the story. There is also a neat eerieness in hearing Spock's voice coming over Kirk's communicator. I also liked the discussion set on the Bridge amongst Kirk, Sulu, Uhura and Chekov. I also liked the original design of Kara's ship. The fundamental story of this episode even if it's sadly botched in overall execution.
“And The Children Shall Lead” - The chilling moment when Kirk and Spock realize they've just beamed two security guards out to their deaths in the vacuum of space. The discussion between Kirk, Spock and McCoy in Kirk's quarters regarding the history of and recent events on Triacus.
“Whom Gods Destroy” - The death of Marta was appropriately chilling in light of Garth's insanity.
I certainly have my choices of episodes that let me down, but even in those dim moments I've usually been able to find something that I still liked...if only there could have been more of it.

At any rate why don't we take a shot at citing something we liked in episodes we were otherwise disappointed with?
“The Apple” - Yeoman Martha Landon kicking ass. Seriously the entire series could have used a bit more of the female contingent of the Enterprise crew mixing it up.
“Spock’s Brain” - There are some genuinely dark and chilling moments in this episode, but they're mostly in the early part of the story. There is also a neat eerieness in hearing Spock's voice coming over Kirk's communicator. I also liked the discussion set on the Bridge amongst Kirk, Sulu, Uhura and Chekov. I also liked the original design of Kara's ship. The fundamental story of this episode even if it's sadly botched in overall execution.
“And The Children Shall Lead” - The chilling moment when Kirk and Spock realize they've just beamed two security guards out to their deaths in the vacuum of space. The discussion between Kirk, Spock and McCoy in Kirk's quarters regarding the history of and recent events on Triacus.
“Whom Gods Destroy” - The death of Marta was appropriately chilling in light of Garth's insanity.