I've been wondering about the difference between television with episodic plotting and programs that develop a story arc. In other words, a program that introduces a new situation and set of characters every episode versus those with a running narrative. I seem to be losing all interest in television that's entirely episodic. I like to invest in characters and plots, and to have them replaced after every forty-five minutes is too jarring. There's nothing to compell me to keep watching, it just adds up as a series of individual stories. An example of this would be the X-Files, a show that I watched three and a half seasons of and then just left. Mulder and Scully are always in a new place, investigating new people - there's no consistency of place or character. The occasional arc episodes do have an impact on the characters but the isolated episodes don't seem to change them, it's like they never happened. I remember them being stuck on a ship, aging rapidly until their skin was rotting and losing all hope of survival, then in the next episode they never mentioned it. I need to believe that these are real characters having important experiences.
Some shows have a consistent location with obvious character arcs but can still feel episodic. In ER there a main characters that go through seasons with the same problems but still deal with isolated issues. People come in with a broken head, they live or they die, but it doesn't really matter because next episode it'll be somebody else with a broken head. Maybe this is unfair, patients can't stay in a hospital forever, but they could have tried a little harder to disguise it. A show that gets the blend between episodic and arc right is The West Wing (and never mind for a second that I think it's the Best Television Ever). Occasionally (usually during the middle of a season) a problem is brought up and dealt with entirely within the episode, but it often has consequences, or is at least mentioned later on. The majority of episodes deal with shifting story arcs, with characters that don't forget things. Sometimes it's an election, sometimes it's something more subtle like Bartlet's psychology.
And then there are the shows that are entirely arcy (that's an adjective now). The Wire sees itself as a visual book with chapters instead of episodes, it builds up one story a season that ultimately gives greater rewards. It's more powerful to see a character's demise after thirteen hours rather than forty-five minutes. Maybe the creators make the point too strongly ('Are you paying attention? If you're not paying attention you won't understand our intricate plots. Make sure you're paying attention. Are you sure you're paying attention?') but it's something I'd like to see more of. And it's proven that it can work over a longer season, with the whole point of 24 being the insistent cliffhangers.
There are a few shows that can work with an episodic structure (Doctor Who manages it, I don't know how) and others that go right to the other end of the scale, like Lost. Most shows find a happy middle ground though. Battlestar Galactica, Buffy, Dexter, Firefly - this is all good television.