This is the final season of ER. Some of the past stars of the show are confermed to make guest apperances. I will put what I know in SPoiler tags just in case you don't know.
Noah Wyle, will return for 4 episodes as John Carter, and in at lest on flashback episode Anthony Edwards will return as Mark Green, also in that episode will be Paul McCrane as Romono,Laura Innes as Kerry Weaver and Abraham Benrubi as Jerry. Rachel Green will be returning(Unknown wether it is the Oringonol or the Recast one) as a first year med student.
Offers have been made for many of the former stars to return including George Cloony and Julianna Margulies to return for the finale.
Now then, how will it finally end? Should a bomb go off and distroy the hospital, should things go off status que, Should the hospital get shut down, or could this be in the imagination of a kid?