At least Life on Mars is ending for a good reason. The show's creators decided that two seasons was enough time to tell the story of the 21st century detective who was hit by a car and woke up in 1973. It's not enough time to satisfy my craving for '70s-style cop shows, but I appreciate their knowing when to quit.
I wonder if the American version will be as wise.
The second season of the British version started yesterday, but no word yet on when we'll get it on BBC America.