Been rewatching a bit of TOS this week. Space Seed, City on the Edge of Forever, Balance of Terror, and other favourites. I think this time watching the show really crystalized so much, aesthetically, stylistically, why I think TOS stands apart from the other shows for better and worse.
First, the colour timing. Every subsequent series was shot with modern technology to some degree. The lighting is very flat. It makes the subsequent series' look cheap, or at least like TV. Comparing the TNG films to the TNG series you see how much the lighting benefited from time and money. TOS doesn't have great lighting either, but what it does have is very stylized, impressionistic color timing. Everyone has a rich tan, the makeup is very pretty, all the colours seem kinda... milky? Everyone has very deep eyes you can stare into, Bones especially who has that Paul Newman radioactivity to his baby blues. This is exacerbated by the garish 60s set designs (lots of pale green paint and bright carpets in set shots, red doors, multiple different colours of lights in the same room, etc). I'm not sure that it looks aesthetically more pleasing, but it looks so distinct. The cast wears very exaggerated makeup; Spock frequently has blue or purple eyelids, everyone's cheeks glow red. Women are frequently shot in soft focus. It just has a very stylized character that the subsequent shows lose.
Second, most episodes do not have B or C stories. In addition, the show runs 6-8 minutes longer than any of the subsequent shows due to differences in commercials. Finally, only Kirk, Spock, and Bones are main characters. The consequence of this is that episodes feel a lot longer and deeper. Scenes feel like they linger more. And many episodes feature a red shirt given significant development. In TNG and later, while you occasionally get named red shirts, and generally each episode has at least an alien of the week characters, you get to know a lot fewer of the crew members. Because every TNG episode had to have an A-B-C plot structure, each normally involving 1-3 of the core cast. Stuff feels more cramped and while we get to know the main cast over the run of the series, I feel like we have less of the world around them. I feel like the added space also leads to better character development for any one-off. Uhura, Scotty, Chekov, and Sulu feel more like Guinan, Q, and Lwaxana in terms of their involvement. One of the reasons why Khan is such a rich villain to draw from in TWOK is because Space Seed gives him quite so many scenes to chew the scenery and build himself up. Balance of Power is even more palpable, it's basically a character study of Kirk and the Romulan captain. We rarely see this in subsequent shows--occasional episodes, yes, but not in general.
Third, the writing is very different. I think the series drew more from magazine sci-fi. There's a lot of really, really clumsy dialogue (typical of TV at the time)--in Star Seed, the transition from "The ship is from the time of the Eugenics Wars" to an a propos of nothing "My Father, The King" dialogue explaining to the audience if not the crew what the Eugenics Wars were--but it just generally has a dreamier, more imaginative tone. There's a lot of philosophy, politics, and social themes in TNG, DS9, and Voyager but I feel like TOS comes almost directly from the magazine era of big questions sketched out very briefly.
I don't know if I've quite captured it, but I feel like this time through that I am closer to getting why TOS "feels" different to me.
