Thursday nights will never be the same without “ER.” For 15 years, I cared about the lives and loves of the doctors and nurses at County General, the everyday chaos and drama in a Chicago emergency room. I loved medical shows “St. Elsewhere” and “Chicago Hope,” but “ER” goes down in history as the landmark series, one that continued to be fulfilling in its final season. John Wells, one of the series creators, paid hommage to the essence of the show was a fitting, graceful finale. Nothing fancy, just solid storytelling. Old characters returning, topnotch guest turns by Alexis Bledel and Ernest Borgnine. Rachel Greene, Mark’s daughter now a bright-eyed 22-year-old medical student, brought the show full circle, and Carter’s last line — “Are you coming, Dr. Greene?” — as the hospital team got ready for another onslaught, the cameras pulling back for a magnificent shot of the hospital, the heartstopping original music coming up, was perfect.