the story: The crew encounters a derelict ship and attempts to figure out what happened to its crew.
what it's all about: Actually, describing the episode like that is actually a selling point for 'Fight or Flight," and how it relates to Enterprise and contrasts with many similar episodes throughout the franchise. Usually, it's a setup for an episodic mystery of no lasting importance. Here, it helps set the series apart and justify its premise. Granted, in keeping it an episodic experience, never following up on either the mystery assailants or the Axanar they come across (the Axanar are a relatively known species in franchise lore, but never really explored), its impact is diminished.
While the crew's responses to the events are pivotal to the episode, it mostly follows Hoshi, who's depicted as the most reluctant officer to be traveling on this voyage. Her scenes can come across as obvious (the slug analogy) or even cloying. But if you can get past that, it really is the crew in general being tested here, and thus the inexperience of Starfleet itself. It just seems too tentative an episode to be the first regular one of the series.
franchise- It's a nice contrast to similar episodes across every series, but if you don't realize that it is, you probably won't notice or appreciate the fact while watching it.
- series - Which is a good thing, because that means it's successful in drawing on its Enterprise context.
- character - Hoshi has the uncomfortable distinction of embodying the inexperienced Starfleet around her.
essential- There's a lot of missed opportunities in its wake, in that it ends up existing in a vacuum in a series that was generally good at closing such loops.