Used to be, your television heroes explored the edges of the universe and confronted unimaginable nightmares. And then they'd end up back where they started. Now television gives us arcs, that continue from week to week. Is that really better?
It's the classic trade-off: on the one hand, self-contained weekly episodes are newbie-friendly and easy to show in reruns, because it doesn't matter what order you show them in. On the other hand, how deep can your characters and universe really get when nothing ever changes and the situations get fully resolved within 43 minutes?
You probably already know the story of how television shows got arced: It used to be that every show was like the original Star Trek, with a neat resolution (and, usually, forced laughter by the main cast) at the end of each episode. And then shows like Blake's 7, Buffy The Vampire Slayer, Babylon 5 and Star Trek: Deep Space Nine (among others) experimented with having more long-running storylines even as individual episodes usually told a standalone story. At last, we ended up with shows like Lost, where an individual episode may just add one tiny pebble to the overall zen rock garden, with no resolution whatsoever. And yet, some shows are still stubbornly episodic, and others try to find a balance between long-term storytelling and singleton episodes.
Really, every show finds a balance — even shows that land really far one end or the other. Nobody is doing pure arcs, nobody is really doing 1960s-style interchangeable episodes any more.
And yet that balance shifts constantly, for individual shows as well as for the television landscape as a whole. Almost any time you hear television showrunners being candid about their arguments with the networks over the direction of their shows, the standalone-vs-arc thing comes up. Watch the unaired pilot of Dollhouse, and you'll see a show that's setting out a ton of long-term storylines in its first hour — but Fox wanted Joss Whedon to deliver a half-dozen episodes that anyone could watch cold, without knowing anything about the show. Terminator: The Sarah Connor Chronicles got renewed for a second season, but only on the condition that most of the episodes would stand on their own — hence the wall of messages written in blood, each leading to a different adventure. And according to Wikipedia, one reason Robert Hewitt Wolfe left Andromeda was because the network wanted more self-contained episodes and less mythology. There are hundreds more stories like that.
Some viewers complain about story arcs because they're hard to follow and you have to trust the show's producers not to drop the ball. It's like that trust exercise where you fall and someone catches you — except that you fall, and hope that two years later, someone will still be there to catch you. You trust that the clues and questions dropped in season two will get paid off or explained in season four — and that there will be a season four.
Really, though, both arc-based storytelling and episodic storytelling can lend themselves to tremendous laziness. Bad arc storytelling can consist of nothing but random wheel spinning, pointless melodrama and random "clues" being tossed out, to keep the juggernaut chugging along. Bad episodic storytelling can consist of cookie-cutter plots, the "rinse, repeat" syndrome, and "monster/artifact/whatever of the week." But really, anything can be done badly — even if it could also be done incredibly well.
On the other hand, whenever you hear about producers saying the network forced them to do more standalone episodes, the result is almost always a drop in the show's quality. That's not because standalone episodes aren't as good as complex arcs — it's just that standalone episodes done by creators who wish they were doing complex arcs instead are usually not as good. And often, the showrunners who are most eager to feature longer-running storylines are the ones whose shows are most prone to the "X of the week" problem. (See Dollhouse, Terminator, etc.)
The main point is that today's audiences are no longer willing to believe that someone can meet God, or battle a sentient nebula, or get tortured, or have space amnesia — and then never refer to those events again. An adventure isn't really even epic unless it leaves some mark on you.
On the other hand, there's only one thing worse than a standalone episode that leaves its heroes and universe completely unchanged: a whole, season-long storyline that ends... and then leaves its heroes and universe comopletely unchanged, and is never spoken of again.
Oh, and then there's the faux arc, where standalone episodes are gussied up with little clues here and there. One of my biggest pet peeves about the Russell T. Davies era of Doctor Who was his habit of pretending he was doing more arc-based storytelling than he was actually doing. If the Doctor mentions the "Medusa Cascade" in random conversation half a dozen times, that doesn't make it an arc — just makes it clumsy foreshadowing.
One other generalization occurs to me: shows that offer complete resolution every week tend to be lighter, maybe even fluffier, than shows that draw out stories over months or years. A show that's totally content bringing up a problem and then sorting it out, with no loose ends, tends to be one that's bright and sunny simply by virtue of showing that problems have tidy solutions. A show that tries to show the consequences of decisions over time, and the psychological effects of events, will inevitably go much darker.
One last thought about arcs: they're usually (but not always) the hallmark of more complex, three-dimensional characters. But when those more complex characters get lost in layers of mystification and randomness (the sort of thing Josh Friedman was talking about in his guest post earlier today) then I'm not so sure that's a worthy tradeoff. But the most important thing is to tell a good story — whether it's just this week, or over five years.