Here's another classic that needs little introduction, the "pleasure planet" episode that helped give birth to the concept of the holodeck and Risa, which itself was memorably featured in "Captain's Holiday" (Next Generation) and "Two Days and Two Nights" (Enterprise), to name a few.
"Shore Leave" is the earliest episode to just let the series have a little fun, perhaps playing off a little from the "Naked Time" effect of seeing the characters in situations that are wildly beyond the norm. There's a lot of Alice in Wonderland to the events, and even one of the earliest fake-outs (He's not dead, Jim!). This lighthearted tone showed the true variety of material available in the setting.
There's also some of the requisite Kirk's-former-associates-were-shmucks material (seriously, it seems the guy didn't catch a break until taking command of the Enterprise!), with Academy classmate Finnegan this time. I'm sure McCoy gained a few more fans from the episode, too. It's a rare opportunity to see him just relax (usually he's just working off of Kirk or Spock). Of course, he's also the one who "dies" so fans were probably just relieved to see him make it out the other side of the story!
There's nothing to much to say except "Shore Leave" is enjoyable as a relaxing experience. Once you've seen it you enjoy it more the next time, that kind of episode, just a generally happy memory.
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