Searching for the "most representative" Star Trek episode

Whenever I see a conversation along the lines of "what episode should I show my friend/partner/etc. to get them hooked on Star Trek," the suggestions are pretty predictable - your "best" episodes that are regarded to represent the franchise at its peak.

I like to take a different approach, trying to find episodes that I feel are most representative of the series - the "average" Star Trek episode. If you show someone the "best," there's nowhere to go but down, and it can set someone up for disappointment.

In the case of Star Trek, I actually find this pretty difficult, and I don't think I've come up with any that I feel are really good answers, so I'm taking it to the crowd: what are the most representative episodes of Star Trek.

To me, these are the boxes that probably need to be ticked:

• Enjoyable (obviously).
• A conventional structure that doesn't deviate from the norm too much - this is a flexible concept, but I think it excludes things like "Darmok," or "Tapestry," or "In the Pale Moonlight," which are not really conventional.
• Any series is fair game.

What do you think? What are some "normal" Star Trek episodes that would serve as good representation of what the franchise usually is?