Here are my terrible ten. Nine of them are from the third season, I'm afraid.
10. WINK OF AN EYE: too conceptually similar to BY ANY OTHER NAME.
9. ALL OUR YESTERDAYS: no interior shots of the Enterprise.
8. LET THAT BE YOUR LAST BATTLEFIELD: Gorshin runs like Pee Wee Herman. He should be more intimidating.
7. IN TRUTH THERE IS NO BEAUTY: I'm not a fan of distorted nose cams, even if it's Diana Muldaur.
6.THE CLOUD MINDERS: Unexplained ventriloquism from Kirky.
5. THE MARK OF GIDEON: A strange message which I interpreted as pro-disease. The cramped nameless Gideonites can die, and best of all, Odona is saved from the very same disease. Couldn't the population be relocated by Starfleet?
4. AND THE CHILDREN SHALL LEAD: Ultra-wussy Scotty.
3. METAMORPHOSIS: Even if you spell it right, it's really quite atrocious. Digitize James Cromwell into it....
2. REQUIEM FOR METHUSELAH: Out-borings METAMORPHOSIS, plus it thinks we won't recognize M-5 again.
1.THE EMPATH: Twelve minutes of Kirky and Spocko waiting impotently behind a pink force field. And forty seconds of Shatner's enema-commercial close-ups coupled with sensitive music more appropriate for an Ivory Soap advertisement.