Altman claimed that "3 Women" was inspired by a dream he had while his wife was lying ill in a hospital, and the film does indeed work on its audience the way a dream does. It resists literal interpretation, and will probably frustrate any viewer who insists upon tidiness in their movies. It communicates its messages instead through pervasive imagery and tone -- it's not "about" something as much as it's about making you FEEL something, and it does that expertly. This movie will stick in your mind and haunt you long after you've seen it.
If I were forced to explain the film's plot, it would go something like this: Shelley Duvall plays Millie, a rather foolish woman who works in a geriatric physical therapy center, and whose roommate has just moved out to live with her boyfriend. Sissy Spacek plays Pinkie, newly hired at the center and put under Millie's direction. Millie is a pathetic character -- she yammers on endlessly about ridiculously trivial things (like how to make tuna melts) and doesn't realize that everyone around her either ignores her or makes fun of her. But Pinkie nevertheless becomes enamored of her and moves in with her. The third woman of the title is Willie, a reclusive artist who owns both the apartment complex in which Millie and Pinkie live, and a saloon that resembles something from a ghost town. She paints murals of strange-looking mythological creatures engaged in violent and sexual acts. These images recur throughout the film, as do images of water. Everything up to this point in the movie is dealt with in a fairly straightforward manner. But then Pinkie has an accident, and when she wakes up, she's become a different person, causing Millie's hold on reality, already tenuous, to unravel. At this point, the film becomes reminiscent of films like "Persona" and "Mulholland Drive," in which seemingly separate female characters merge into different facets of one female personality.
The ending is creepy and chilling in ways that are hard to define. The whole film has violent undertones -- the lone male character in the film is a lout and vaguely predatory; all of the women at various moments seem to be holding back a barely suppressed rage. Altman uses his camera in his characteristically expert manner to shape our perceptions about what we are seeing, and he uses other parts of his mise-en-scene, like color (Millie's favorite colors are yellow and purple, and look for them in the art direction), to bring a slightly surreal quality to even the most mundane of locations.
I've always thought that Shelley Duvall was an underrated actress, and she gives one of her best performances as Millie (and almost looks pretty for a change). Sissy Spacek is tremendous as well, and shows a remarkable range as Pinkie. Both of these actresses do wonderful things with tough roles, and even if we sometimes feel like we're on uneven footing because of the movie's enigmatic nature, the actresses are so assured in their parts that we can rely on them to guide us through it.
Altman directed a quartet of "dream" films that all revolve around the psychological and emotional crises of women: "That Cold Day in the Park" (1969); "Images" (1972); "Come Back to the 5 & Dime, Jimmy Dean, Jimmy Dean" (1982); and "3 Women." I've not seen "That Cold Day..", but of the other three, though all of them have qualities to recommend them, "3 Women" is easily the best.