What elements in the episodes or movies would you say are the most like fantasy, more like Space Fantasy than just Science/Space Fiction? And of them which do you think worked and which didn't, and why, what was the difference?
B'Elanna descending into the underworld for her mother's soul, part of a tradition going back to Greek legend, if not earlier. I think a necessary component to it working in Star Trek is leaving ambiguity as to how real the experience was.
There sure are a lot of beings out there with massive powers. Trelane. Q. The Traveler. The Talosians. Kes.
In terms of technology, the transporters. I accept them the same way I accept the root premise of "Space: 1999" (nuke splodey causes moon to leave orbit and fly through the cosmos at sublight speed and encounters as ridiculous amount of events... some of which sell themselves impressively well despite it all.) Otherwise, ESP and telepathy - despite being a staple of sci-fi - seem more fantasy than anything else. Indeed, "empathy" is used by Troi 98% as nothing more than "'cold reading' mixed with poker". But being a group with sci-fi and fantasy rolled into one, it's inevitable. It's a spectrum of degrees, not a binary absolute.
And telepaths being able to mentally interface with machines, such as Spock mind melding with Nomad, and Troi sensing emotions from Data. Kor
The Metrons, Organians, hunkylicious Apollo, and about 50~80% TOS aliens, hehe... either as glowing balls of light or brains separated from bodies but developed psy powers and teleportation from half a galaxy away... or that one from season 3 that's a big rock with arms and legs that conjured up Lincoln and frenemies/w/benefits... How Troi can sense emotions from a positronic computer... positronics is a theoretical construct using positrons instead of electrons... would they really emit emotional waves in the way electrons and silicon(e)-based lifeforms don't?
"The Magicks of Megas Tu": at the centre of the galaxy is a portal to a universe where magic was real. You cannot top that. Spock draws a pentagram on the rec room floor and moves chess pieces with his mind. I love it.
Honestly just the speed with which they are able to diagnose and research and fix different things. And the variability of travel/communication times. Same thing with weapons that fire/move too slowly. ...so “time” is a major problem realism-wise. Might as well be “magic” finessing it all.
TNG had a fair amount of therm too, The Douwd, Cytherians, Nagillum, etc... But if we're looking for the most fantastical thing about that kind of premise, it has to be that not only is the galaxy positively littered with supernaturally gifted beings, but humans are naturally evolving to that level of existence themselves, beginning with none other than our own Wesley Crusher
When it comes to fictionalized material they work for me as long as they maintain and continue their own rules within the confines of that universe. What an invention to crystallizing lithium? Until Dilithium came around.
When first invented, the government first used simplistic jargon for the "hydrogen bomb", not using the more correct term like the "deuterium bomb"...and I guess today they call it a "fusion bomb" to be more technically precise. In fantastical physic's talk, maybe they first used the simplistic jargon of "lithium crystals" since its discovery, but during TOS, they had a revolution is technical preciseness and started calling it by its more correct fantastical physic's jargon, "dilithium crystals".
And the fact that half the time, they know how long repairs will take before they fully diagnose the problem. If you don't know what the bug is, you don't know the extent of the modifications you'll have to make and the time it'll take!
Fission fusion bomb, no one has ever been able to make a "pure" fusion bomb.. By which time all Humans will be salamanders. Scotty would over estimate his repair times three.