or how about just an episode that presents serious ethical / philosophical / moral dilemmas that leave open ended interpretations, holds a mirror to our current society, provides personal introspection and generally just makes the viewer think critically of the world we all live in.
I think what people forget as in the nu trek writing staff is something Ronald D Moore said about writing for TNG. Star Trek was one of the few shows that where they could do all the genres in a single season. One day it would be a western the next it can be a medical drama. The next a courtroom drama.
Most of the new shows it's the same story every season. There is a MacGuffin, the crew does a scavenger hunt to find said MacGuffin and that MacGuffin saves the universe.