Last year a lot of the new US dramas were highly serialised - meaning that you have to watch them every week to follow what's going on. They've traditionally tended to steer clear of this in Prime Time, as the Yanks have a hard time watching every episode (they're wierd scheduling probably doesn't help)., but the success of shows like "Lost" seemed to suggest that maybe it was possible not to have stand alone episodes (like CSI tends to be).
It seems that the American public didn't agree and a lot of shows went to the wall. at least (AFAIK - I haven't had time to watch more than the first few eps) "Kidnapped" and "Vanished" got some warning and were able to at least partially wrap up - others just ended! Mind you, some of the concepts seemed good as limited series, but I'm not convinced that they would have worked for more than one season. I'm gutted that we'll never find out what happened in the bank in "The Nine", or who won the race in "Drive".