His breakthrough M*A*S*H film was made more or less at the same time as other mainstream war films like Catch-22 and Patton, but his had a humanistic twist, not as black as Catch-22, not as jingoistic as Patton. The characters were iconic, and the setting eternal. So much so that the TV series that followed used the same set, ran for a record time and was much loved. Altman did not see much or any money from the series.
It is interesting to compare the movie to the series. It is a good example of how movies could go further, were more adult, in the real sense than TV. The sentimentality was absent, the self-censorship not there.
Fast forward to about ten years ago. Altman, in his mature years, make the perfect manor mystery: Gosford Park. The threads of social change in post Victorian England are captured. The futile snobbery, the emergence of movie making, the dark side of robber barons, and the unfairness of class, are all wrapped in the tropes of the genre, with a wink at the detective, hammed up by Stephen Fry, the upstairs downstairs, the shooting party, the sumptuous settings. The movie works, like all Altman movies, on so many levels that it almost becomes a documentary.
The script credit goes to Julian Fellowes, who afterwards, said that Altman took his script as a starting point, in the same way that Kubrick took Clarke's "2001 a Space Odyssey" as a starting point (my interpretation, not Fellowes').
Fellowes got a hefty fee with which he bought one of the manors used for the set. He then famously went on to write the TV series Downton Abbey, with many of the same characters and settings. It is a lavishly produced soap opera. Sentimental, full of short intertwined plot lines, but ultimately apologetic to and for the upper classes. Completely unreal, completely different than Gosford Park, hugely successful and profitable.
Downton Abbey is to Gosford Park what the M*A*S*H television series was to the original movie. Altman's career was framed by two very similar show trajectories.