This article is from the ER FAQ, by Rose Cooper firstname.lastname@example.org with numerous contributions by others.
"ER" is a weekly one-hour television drama on NBC that takes place
in the emergency room of a Chicago hospital. The show`s stories focus
primarily on the staff of the ER: doctors, nurses, medical students
and assorted personnel. The stories secondarily deal with the medical
problems of patients. "ER" is unlike most other medical dramas in that
its emphasis is often on a very fast-paced style of action, typically
when a patient or patient(s) is/are rushed into the emergency room for
treatment. It does share some similarities with other medical dramas,
however, particularly St. Elsewhere, in that stories in the lives of
the main characters are told over the course of many episodes, rather
than being self-contained to one episode.
[Given the general direction that Season Four veered toward, it remains to
be seen whether the above will still hold true for Season Five--and beyond...]