At the time ER debuted it was the "It" show, meaning it was the show that, the day after it aired, people would talk about at work or school and even on talk radio. It instantly became the hot show of the season and a ratings giant for NBC. It told the story of a Chicago hospital, just known as County, and told the story of the doctors, nurses, and staff who worked there. It started out somewhat being told through the experience of a third-year medical student named John Carter (played by Noah Wyle) as he began the "hands-on" portion of his medical school training. The show had a true ensemble cast made up mostly of (at the time) lesser-known character actors. The most recognizable member of the cast at the time the show debuted was Anthony Edwards (who had been in Top Gun and had just come off a stint on Northern Exposure). Of course, cast members like Noah Wyle, George Clooney, and Juliana Margulies would go on to have huge careers after their run on ER, as would actors like Ving Rhames, and William H. Macy, while other actors like Laura Innes, Paul McCraine, and Eriq La Salle would transition from actors to directors after their time on the show.
The show can really be seen as two series. The first eight seasons and the final seven seasons. By season 15 there was an entirely different cast as new cast members were brought in to replace those who left. A few members of the supporting cast (mainly those who played nurses) did stick around for the entire series run, but pretty much all of the actors who played the doctors had turned over by the time the series ended. The show focused on all sorts of issues over the course of its run including drugs, AIDS, abortion, crime, racism, mental illness, and more. Sometimes there were cases of the week that took up most of the hour, other times it was just chaotic turnover in the ER with a show involving multiple storylines. The show took a lot of risks, including airing a live episode, killing off main characters, and generally putting characters through the wringer. An argument can be made that it did start to get stale by the end of its run, but overall it was a very well-written and well-acted show. And, the final season did manage to bring back some of the original characters to give those of us who watched at the beginning a boost of nostalgia. It also boasted a ton of guest stars who would become A or B list actors, including Mariska Hargitay, Ewan McGregor, Ron Eldard, Kristin Davis, Stana Katic, Kirsten Dunst, Lucy Liu, Thandie Newton, and Kat Dennings, to name just a few. And, some of the guest stars were already well-known, such as Rosemary Clooney, and Michael Ironside, Ron Rifkin, and Alan Alda.
There are a few different versions of the complete series set, but they all seem to just repackage the individual season releases. So, you get all of the bonus material that was originally released with the individual season sets. The bonus features varied from season to season, tailing off toward the end of the series as TV series on physical media were just starting to get cut back in favor of just streaming them. But, there were commentary tracks on some episodes, cast interviews, blooper reels, and the like, over the years. The series has not been released on Blu-Ray, and it would be a surprise if it ever gets one. Some older shows are getting Blu-Ray releases so it is not totally outside the realm of possibility that ER will get one someday, but it is unlikely. It is on multiple streaming services including Hulu and Peacock, so really, the decision of whether to shell out for this will depend on if you want to watch the DVD extras. It is definitely one of the best medical dramas that have ever been made and still holds up nearly thirty years after it originally aired and thirteen years after it ended