There are only a handful I skip - off the top of my head they are Gamesters, Is There In Truth?
These are two bad episodes I love to watch over and over.
Is there... has a lot going on, not least of which is people's hidden motivations. People do things completely against expectation because of their own petty (not so petty to them) jealousies and desires. As a youth, and younger person, I hated this 'boring' one. Now I love it.
Gamesters is just pure schlock, plenty of skin, and Kirk fights a lot. Awesome.
Whom Gods Destroy is my all time favourite BAD one. Ihnat, as Garth, is superb. Lines like "I may have you beaten to death," and "I'll kill you with my bare hands!" never fail to amuse. He and Shatner throw great overacting tantrums.
Love it.
Spock's Brain and The Way to Eden are camp fun of the highest level.
The Alternative Factor, And the Children Shall Lead... I jsut can't stand. I never watch them.