Stephen King in EW--in the snazzy 24 pull-out section--gives us the formula for high-concept serial TV:

24 is a perfect example of why some serial TV works and some doesn't. The audience will come along for the ride, but it requires certain things as a quid pro quo. One is an element of believability (which ABC's Invasion never supplied). Another is what producers sometimes call ''a clear through-line.'' What this high-toned bit of jargon actually means is simplicity (NBC's Kidnapped threw that out in the first five minutes of its abortive run). Another is a high emotional temperature (which ABC's The Nine managed for exactly one week before lapsing into soap opera torpidity). Continuing stories have to run hot. How 24 has managed this kind of heat for six seasons is beyond me.

Last — and here's the genius part — continuing series must provide some degree of closure; the audience must feel they are getting somewhere. One of the reasons Lost may have suffered in the ratings this season (although suffering in TV is relative, and many struggling shows would kill to have Lost's ratings) is because it somehow misplaced that sense of things rushing toward some sort of conclusion. Even Fox's Prison Break (a column on this wonderful and hilarious show is forthcoming) provides that sense of closure; at the end of the first season, the main characters broke out of prison (well, duh). Now that the actual prison break's over, season 2 should be titled Show Me the Money.