76th: Plato's Stepchildren. This episode is deliberately embarrassing and that's hard to take.
77th: The Savage Curtain. Lincoln comes aboard? And then we fight weirdos for the edification of a rock monster? I'm stunned at how few others here have listed it.
78th: And the Children Shall Lead. The children are annoying, and the story uses a fantasy plot device to rationalize having characters behave in ways that real people never would.
79th: The Alternative Factor. The actor cast to play Lazarus went to lunch on day one and never came back. The producers had to scramble like crazy to bring in Robert Brown to play the part with no prep whatsoever, not knowing his lines, and no time to put together a decent look for his character-- and it showed. The whole episode was a trainwreck in production and it's hard to follow with all the Lazarus-switching.
If they'd had another week to iron things out, "The Alternative Factor" could have been a lousy episode like "Let that be Your Last Battlefield" or "That Which Survives." But there was simply no time to solve the problems, and the result was a wooden, jumbled, terrible episode.