SFX gets dated, but good writing and acting is timeless.

Want both?

Battlestar Galactica: Come for the battles, stay for the moral quandaries

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.

Or generally an episode where they just have some people talking a bunch so they can save on special effects. (DS9’s Duet comes to mind.)