After 15 seasons of fixing patients and breaking hearts, the doctors of 'ER', the television drama that launched superstar George Clooney, booked their final appointment on Thursday.

The 332-episode, multiple-award-winning series closed on NBC with a two-hour special that ended at 11 pm in the US.

Blood-soaked drama returned for the finale, with an older man watching his lifelong sweetheart die before his eyes and a mother dying after giving birth to twin girls.

But hope was also present, as the daughter of Doctor Mark Greene looked poised to take over her late father's profession. As she looked over a bloody scene, someone called out to her: "Dr Greene?"

The popular Doctor Greene, played by actor Anthony Edwards, died of brain cancer on the show in 2002 after eight seasons as a pivotal character.

Television critics praised "ER," set in the emergency room of Chicago's fictional County General Hospital, for its ground-breaking style, brilliant casts and staying power.

"It's the longest-running medical drama ever. Just in terms of pure popularity, you have to go back to the 1960s and the glory days of 'Bonanza' to find an NBC hour to match," the Hollywood Reporter said.

Starting in 1994 on the basis of a script by Michael Crichton, author of 'Jurassic Park', 'ER' immediately set pulses racing with an eye-catching cast that included now famed actor George Clooney playing Doctor Doug Ross.

They broke some hearts and warmed others in overlapping story lines capturing the hectic and harrowing life of an ER unit.

Famous for fast pace and moving camera shots, the show "blazed an unprecedentedly realistic depiction of the visceral, pressurized practice of emergency medicine at a big city hospital," The Philadelphia Inquirer said.

For some critics, 'ER' was a victim of its own success, sticking around too long as ratings slid from spectacular to acceptable.

The premiere generated an audience of 23.8 million viewers and four years later, in 1998, a record 47.8 million viewers tuned in. Last week it was still NBC's most watched show, but only with 10.3 million viewers and 20th in weekly primetime rankings.

"It's about time 'ER' is taken off life support," USA Today said.

"Imagine how much more heartfelt the celebration would have been had it departed six or seven years ago, when it was still in sight of its creative heights."

The final episode was preceded by a one-hour retrospective in which actors shared their favorite moments on the show.

The show's current headliners include John Stamos as a "flirtatious paramedic who also is a medical student and a Gulf War veteran" and Angela Bassett as "tough-as-nails attending physician Cate Banfield," NBC said.

In anticipation of big viewership, the rate for commercials was hiked to 425,000 dollars from 135,000 dollars for a 30-second spot, according to the Hollywood Reporter.

But it will be hard to top the emotional punch for fans in the one-episode return of Clooney to the show three weeks ago.

"We must admit, the 'ER' finale tonight has something of an anti-climactic feel to it," the Winnipeg Sun lamented. "Even if Clooney jumps out of a closet again, it's kinda 'been there, done that,' ya know?"

Still, 'ER's' heroes are likely to be remembered for giving primetime television a healthy injection.

The show racked up 122 Emmy nominations, winning 22, and few viewers were untouched by dramas like Clooney's Doctor Ross struggling to rescue a boy from a flooding drain.

"A lot of things have to go just right for this kind of success to happen," creator/executive producer John Wells told the Hollywood Reporter.

"There's an alchemy to these things when they work. You wind up looking like a genius, but the truth is you can never replicate it."

AFP