Another vote here for "The Empath". The minimalist sets were perfect and allowed the viewer to concentrate on the interaction between the actors instead of being distracted by special effects. Plus I've always felt Katherine Hayes was one of the loveliest ladies to grace the series. Her kittenish innocence was I thought was a marvelous performance.
The Empath seems to have a lot in common with The Cage, starting with the Vians' Talosian-esque giant heads, the created illusion of Scotty and the rescue party, the abduction of "test subjects"...