The film takes place in California in the early 1990s and is about the movie business in Hollywood. Wikipedia describes it as "a satirical black comedy". Undoubtedly, there is an element of strong satire: Robert Altman, as a leading director in America, was an insider, and he gives us a fairly devastating picture of 'creatives' and business people in Hollywood, who, ultimately, are not producing 'art' (as they would sometimes like to pretend) but products (intended to make them a lot of money and to boost their careers). Most of the characters are cynical, greedy and without scruples. On the other hand, is it a "black comedy"? I suppose it depends what one calls a "black comedy". Funny overall, it is not, in my view, although there are funny incidents and situations, and comical characters (but, after all, you get that in real life too). The other aspect of the story is that it is a thriller, but not a thriller that is developed to any degree, in my opinion. In the last analysis, it is a social drama about the American movie industry on the West Coast of the USA.
The central character is a film producer: Griffin Mill (Tim Robbins) is a Hollywood studio executive. His job is to sift through hundreds of scripts of films that he receives (presented as 'pitches'): his company only produces a dozen feature films per year. Many scripts, inevitably, are rejected. In the process, G Mill has made many enemies. G Mill has been receiving death threats, scribbled on postcards addressed to him; he assumes they are being sent by a disgruntled and bitter screenwriter whose "pitch" he will have rejected. Added to this, there is an element of corporate intrigue (within the film studio he works for) and an encounter with a female artist (Greta Scacchi as June Gudmundsdottir). The story develops from here, while G Mill is trying to establish who the person sending him the poison-pen postcards (and faxes) is.
The film is good, but it not the masterpiece we could have expected from R Altman, in my view. I found that it has a range of flaws that prevent it from quite having the impact you would have hoped for. First of all, the film is self-indulgent, self-aware and narcissistic, inevitably, to a certain extent: it is a film about making movies and, despite the element of satire, you can tell all the people featured in the film (in the film and in real life!) are quite pleased with themselves and with their positions in an exciting industry. The movie probably features the longest list of cameos involving film stars ever put together, as Hollywood celebrities agreed to pop in as extras at R Altman's request, as he knew everybody in Hollywood - among them Cher, sporting a striking red dress. Second, there is something a bit superficial about the story and its development; in a way, the funny moments deflate the tension and tend to break the pace of the story: they make it more difficult to take certain incidents seriously, as it were. Third, in my view, the character played by G Scacchi, who is an excellent actress, is a blank page: we hardly know anything about her, beyond the fact she is a good-looking artist from outside the USA. This weakens the plot. Fourth, I found the ending a bit of an anti-climax, but I cannot say anymore than that, obviously.
In conclusion, it is a good film and I enjoyed watching it; I would recommend it. But it is not as good as it could have been, or as most reviewers claim: it is a bit shallow, somehow, but, perhaps, this is something R Altman wanted to show, precisely, i.e. that this is what the film industry ultimately is. Compare it to "Once upon a time in Hollywood" (2019), which is, in my opinion, far superior.