+++Warning, this contains spoilers from prior seasons and minor spoilers from the final season+++
ER's 15th and final 22-episode season aired during the 2008/1009 TV season. It marked the end of one of the longest-running, and best medical dramas ever. There was yet more cast turnover this year with Mekhi Phifer, Shane West, Maura Tierney, and Goran Visnjc leaving the show as series regulars. Some would appear here and there throughout the season, and some had a one-and-done appearance. Angela Basset was the big addition to the cast, joining as the new Chief of Emergency Medicine, Catherine Banfield. The show also had several recognizable guest stars throughout the season including Tony Hale, Chadwick Boseman, Carl Weathers, Ariel Winter, Wallace Shawn, Rooney Mara, Ernest Borgnine, and Judy Greer, among others.
I have always looked at ER as two different series. One that lasted through season 8 when Anthony Edwards decided to leave the show and the one that remained on the air until the end. Personally, I would have liked to have seen the show end after the 8th season, because had the shows that told the story of Dr Green's death been the series finale, the show would have gone out on a high point and would have never been accused of hanging on too long. This season really tries to bridge the two series, by bringing back many former cast members, including Edwards, Paul McCrane, Laura Innes, William H. Macy, Thandiwe Newton, George Clooney, Juliana Margulies, Alex Kingston, Sherrie Stringfield, and Eriq La Salle. The catalyst for bridging the early seasons to the later seasons was a storyline involving Dr. Carter that extends throughout most of the season (Wyle returns as something between a recurring character and a series regular). Edwards and McCrane are brought back in a flashback episode that found a creative way to include Basset's character. For those who were fans of the show from the beginning in 1994, the season provides a shot of nostalgia, while also wrapping up the storylines for the current main cast members like Scott Grimes, John Stamos, Linda Cardellini, and Parminder Nagra.
The DVD set is a six-disc set. It has a handful of special features including unaired scenes and a series retrospective with interviews with cast members and showrunners. Given the impact the series had, launching (or helping to launch) the careers of many stars (including Clooney, Margulies, Ewan McGregor, and Ving Rhames, to name just a few) as well as having many notable guest stars, it should have had a lot more special features looking back on the series. Even so, what was included is good.
The season was very good, and one of the best in the season 9-15 era of the show. It was very nice to see the old cast members even though some just had cameo appearances. Many people complained about the episode in which Clooney and Margulies were brought back for having a totally unrealistic story. I think it was the best that could be done to give Clooney his "own" episode where he and Margulies could do more than just make a cameo appearance in the finale like Sherry Stringfield, Alex Kingston, and Laura Innes did. While the storyline was contrived and would not happen in real life it was really the only way, aside from having Carter go out to Seattle, to have a reason for someone from County to be interacting with Ross and Hathaway. Given that Clooney was really 1a and/or 1b along with Anthony Edwards and Margulies was a major star on the show in the early years, I think it was better to do what they did so the two could be in more than just one or two scenes. I also think the way the show ended, with Morris (of all people) taking over as the lead character, and having Carter passing the baton (so to speak) to Dr. Green's daughter who had become a prospective medical student, was the best way to end the series. It was perfect to have Noah Wyle be the last person we see on screen since the show started with his character as the wide-eyed medical student back in episode 1.