There are many lists with recommended/must-watch episodes. But they usually just include episodes that are considered good or great.
Is there also a list with episodes that are important but not necessarily good? By important I mean episodes that introduce new concepts or new characters (or kill off important characters), or that have lasting repercussions in the overall story of the series or Star Trek as a whole, or are necessary to watch first for a pay-off way later.
For example, TNG’s “Skin of Evil” shows the death of a main character but it’s hardly a good episode. The same goes for DS9’s “Life Support”. I wouldn’t exactly call ENT’s “Storm Front” good either but it’s important to cap off the temporal cold war. TNG’s “Ménage à Troi” shows Wesley being promoted to Ensign but the rest of the episode is rather mid (except for the Picard meme) so that it wouldn’t ever appear on any must-watch list. etc.


You’re right. Your list makes it quite clear that when the bar for importance is too low, 90% of all episodes end up being important. From season 1 I’d include 5 episodes in the list of important episodes: Encounter at Farpoint (setting up Q and everything), Where No One Has Gone Before (introduces the Traveller), Datalore (introduces Lore), Skin of Evil (kills of Tasha), The Neutral Zone (Romulans and Borg implied). Those episodes are a good example of what I was going for: none of them is above average but they’re still important. “Where No One Has Gone Before” maybe comes the closest to being good.
Sidenote: I recently rewatched TNG season 1 and found it oddly charming. There are a lot of bad episodes but almost every episode had something going for it. You could see what they were aiming for but often couldn’t stick the landing. And the music was really great, unlike in the rest of the Berman era.
I would add Heart of Glory because it gives a crucial introduction to where the Klingons are as a society in the 24th century much as The Neutral Zone introduces the state of the relationship with the Romulans (and sets up the Borg threat).