I’ll start talking about actual episodes and content soon enough, but before that, I’d like to look at the general format of the show. (No spoilers, really, but I’ll put it behind a cut for length anyway.
This show runs on that workhorse of a narrative engine, the Monster of the Week. In this case, quite literally monsters: virtually every episode centers around “here is some bit of bad supernatural weirdness going on.” You know that by the end of the ep, the Winchester brothers will have identified and dealt with the threat. It’s the “case file” approach, and its advantage is that it can run from here to infinity, so long as you’re able to keep on thinking up new cases.
Of course, the downside to it is that it gets repetitive. This summer, when I was teaching creative writing to a bunch of gifted twelve-year-olds, my students got into a discussion about books they had loved. One of them mentioned a series — I don’t remember which one — and said “I used to read stacks of those things. I didn’t even notice they were all the same.” When you’re young enough, or (for one reason or another) uncritical enough, you don’t mind repeating the same dance over and over again. But eventually that palls, and so you wander off to look for something new . . . unless the writer is doing enough besides the formula to keep you hooked.
Sometimes you can do this with sheer plotting: making each case twisty enough that the audience doesn’t mind the rinse-and-repeat effect. Sure, it’s another beastie and you know the brothers will defeat it by the end of the episode, but the interesting part is how they get there. This one is exceptionally difficult to pull off on a long-term scale, though, because twisty clever plotting is HARD, YO. Doing it every week for years? Yeah, good luck with that.
Supernatural mostly doesn’t rely on this sort of thing, though the occasional episode will feature a neat bit of narrative jiujitsu. They go for Door Number Two: character. As a teenager, I did not mind that David Eddings’ Malloreon series was the Belgariad put on loop, because I loved the characters so much I would gladly pay cash money to watch them ride across the map again, snarking all the way. (Even today, I still find them amusing.) Many case-plot shows live or die on the strength of their characters — and this one more than most, because the core cast consists of a whopping two people. This gets expanded a little bit over time (Bobby, and then Castiel, and a few other recurring characters), but ultimately it’s about the Winchester brothers. They are the engine that makes this thing go, and if you don’t like them, you pretty much have no reason to watch the series.
Back in the good old days of TV (which is to say, the days before Hill Street Blues changed TV storytelling forever), that would have been the end of it: Odd Couple protagonists, a case each week, and you’re done. Nowadays, of course, we look for more. So it isn’t just the Sam-and-Dean dynamic that keeps the Monsters of the Week from getting old; it’s the long term development of Sam, Dean, and Sam-and-Dean, along with their relationships to other characters and the world around them. Those two change over time, at least to a limited extent, and that change is part of a feedback loop with the episodic case plots: who they are affects how they approach things, and the things they encounter change who they are. In the earliest episodes, Sam is entirely fixated on finding his father, and annoyed at how the cases distract from what he sees as his real goal. Soon, however, he’s changed his tune: first he accepts that finding John will take a while, and in the meantime he might as well do some good; and then hunting bad stuff becomes a goal in its own right.
Speaking of finding John . . . let’s talk metaplot.
Or rather, let’s start talking metaplot, since it’s a topic we’ll be coming back to again and again. That’s the final piece of this particular formula, and if it didn’t start with Chris Carter and the X-Files, that man and that show certainly left a giant mark on this one. Right there in the pilot episode, the script makes a nod to its X-Files debt (when Dean refers to the two agents at the bridge as “Mulder and Scully”), and several episodes are pretty direct analogues of Carter’s work. But unlike The X-Files, this show doesn’t try to string out its core questions forever. They get answered, and the answers generate new questions, so that season 3 isn’t about the same things as season 1, and season 5 is different yet again. But it isn’t the kind of bait-and-switch J.J. Abrams is (in my opinion) too prone to, either: there’s no screeching left turns, just a series of dominoes of increasing size.
So when the show gets rolling, they’ve got a nice three-layer cake of plot to work with: the short-term goal of whatever monster Sam and Dean dealing with this week, the medium-term goal of finding John, and the long-term goal of identifying and taking out the creature that killed their mother, i.e. “the yellow-eyed demon.” (Azazel doesn’t get a name until late enough in the game that I just think of him as the yellow-eyed demon, since that’s what they call him most of the time.) Put it together with the buddy dynamic, and it’s a good, solid framework on which to hang the specific content. For an American TV show, that’s crucial, because they have to fill a lot of episodes each season. It’s valuable in other contexts too, though — anywhere you’re trying to balance the needs of an episodic format with the longer-term development of a larger plot.