I felt like watching some classic Trek today so I pulled up Season 1, Episode 1 ("The Man Trap") on Hulu today. "The Man Trap" might be better known as "the Salt Vampire" episode.
After having not seen this one in years (if not decades) I was surprised that, a few hiccups (Uhura trying to flirt with Spock and an incredibly cheesy plant puppet) notwithstanding, the first episode established a lot of what made Trek "Trek": A mystery on a strange world, a moral dilemma about species extinction vs human life and a nascent version of the "Kirk/Spock/McCoy" trinity.
I could also see how, back when it first aired, parts of the series could have caught people by surprise. The diversity of the cast was there at the beginning. The opening had Kirk, McCoy and a crew member named Darnell beam down to a archeological outpost for a routine medical examination. The way it was set up Darnell seemed as major a character as McCoy or Kirk but he died pretty quickly (even if he wasn't wearing a red shirt). Later, when the salt vampire is loose on the ship it appeared as if Uhura, Sulu or Rand might get killed like Darnell (none of them were in the opening credits back then and you could have easily assumed all them were just cannon fodder, especially the "minorities."). There was even a moment or two where characters attempted to suggest that the monster might be something that could have been dealt with by more peaceful means if Kirk allowed it.
I'm tempted to rewatch the whole series from start to finish now.
