I'll tell you why I love Out of Gas.
First, the main plot, the 'exciting' plot is a wounded Mal desperately trying to fix his ship before he runs out of air. It's a 'bottle' episode - for those who don't know what that is, a quick sidebar: in Star Trek there were generally only two types of episodes (across all five shows); the 'planet' episode which took place on location/set of a planet and had the characters meeting aliens and encountering weird civilisations and what not, and the 'bottle' episode which took place only on the ship and generally involved the crew getting screwed and trapped in the ship and having to fix the damn thing - which I love and it's 'framed' (it starts at the end and flashbacks). Now, in such an episode, we normally get two things - the show jumps back to before the 'bad thing' and the show steadily progresses towards the beginning; and we also get the feeling that the 'framing' is actually a big fat lie designed to hook us like a fish.
Out of Gas manages to use the tools of framing and flashback effectively, and not as a manipulative cliche. First, the show doesn't travel back to the before the explosion and then play out in a linear fashion. It hops back and forth between flashback and present, simultaneously moving both plots forward and keeping our interest. This is used to such advantage as to make Mal *dropping an item on the floor* so powerful it warrants an act break. Think about that - all Mal does is DROP something. But because of the flashbacks setting up the situation, being cut with Mal having to trek through the ship, wounded, (and with further flashbacks, detailed below), the scene of Mal dropping this piece of equipment is filled with meaning.
Secondly, the show can be told completely linearly and it would still work. Not only that, but the opening of the show - Mal bleeding to death on a dying Serenity - is not, in any fashion, a lie. It is completely what is happening. They don't make it seem worse than really it is at the beginning to hook us in. It is as bad as they say and they use it fully.
If this wasn't enough, through some amazing flash of insight, the writers thought this episode should be the 'origin' episode. So not only do we get the 'bottle' episode alternating in past and present to climax, but we also get the 'pilot' episode as we see the characters meet for the first time. By using these flashbacks in this show they do an amazing thing - they first maximise on the storytelling tools they're using: since they're already using flashbacks, they are using flashbacks to many different time periods since we're already prepared, from the teaser, for a non-linear story (however, with the exception of the very final scene, it's obvious that each of the three time periods - the meeting of the crew; Mal wounded; and Serenity damaged - moves in a very simple, linear fashion so as to keep the story simple) the addition of alternate time periods isn't too intrusive.
But somewhere, someone realised the genius of giving us, to this episode, the episode where Mal is abandoned on a dying Serenity, someone realised that this was the episode to have the characters meet.
What that simple addition did, boggles the mind. By having the characters meet it not only allowed for humourous interactions (such as Zoe's reaction to Wash, or Kaylee's introduction) but by having such a time jump from introductions to the desperate end of their time together we get THEIR ENTIRE STORYLINE in an episode. Think about that. As you watch the show, YOU fill in the gaps from their meeting to their current situation. YOU do that work. Isn't that amazing? And because YOU'RE doing the work, you are becoming very much involved with the story, which makes you care all the more about what's happening. It not only does this, but it also adds meaning to what's going on as we come to realise what Serenity means to the characters, and especially Mal, and in so doing, it comes to mean something to us too.
But it doesn't just do that. No, sir.
Out of Gas also DEVELOPS CHARACTERS. We discover a lot about Zoe and Walsh's relationship, we learn a lot about what type of man Jayne is, we realise Kaylee isn't the little innocent we thought she was - and Mal. Dear God, how much of Mal we get.
So the show works on a structural level with a clever use of flashbacks and multiple sub-plots; it effectively draws its audience into the story; it is rife with meaning and emotion; and it develops characters. This show is one of the best single episodes of tv I've seen.
And not content with all this - they even successfully saved the best for last:
The ending - Mal, lying on the hospital bed, recovering. He's about to go to sleep, he looks up to his crew/friends and says - "You'll all be here when I wake up?"
Of course they will.
And Mal goes to sleep.
And we see the flashback we saw towards the beginning of the episode - of the man who sold Mal Serenity - an obvious pile of **** that doesn't work; claiming it'll outlive him. We hear the man's sales pitch and we know he conned Mal. Then we see the man is actually selling Mal a huge, shiny, big ol' super ship.
But Mal ain't listening. He's too busy falling in love with an obvious pile of **** that doesn't work that's collecting dust in the lot - Serenity.
This final scene is so beautiful and powerful, and draws all of the themes, stories and characters to one specific point, transcending time and touching the eternal - ironically for such a brief moment - creating a timeless, endlessly repeatable moment of insight, meaning and joy.
While Firefly has many good episodes, and Serenity is quite good too - Out of Gas is an excellent episode that I can watch forever.