Annette Bening gives a charismatic performance in Mike Mills’ semi-autobiographical “20th Century Woman,” but despite many incidental pleasures—including a strong supporting cast—the film as a whole isn’t entirely worthy of her.

Mills, a former graphic designer and advertising man, received considerable recognition for his second feature “Beginners” (2011), which won an Academy Award for Christopher Plummer, playing Hal, a man who came out of the closet in his seventies. The character was based on Mills’ own father, and his late-in-life decision was contrasted with the inability of his son Oliver (Ewan McGregor)—the writer-director’s surrogate—to commit to the woman he loves.

Now Mills turns to his mother for inspiration. She appeared, via flashbacks, in “Beginners,” played by Mary Page Keller. But in that earlier incarnation she was a tangential figure, and a darkly eccentric, even shrill one. Here, as played by Bening, Dorothea Fields remains an eccentric, but a quirkily likable one, a charmingly free-spirited, mildly countercultural soul and single mom bringing up her fifteen-year old son Jamie (Lucas Jade Zumann)—the Mills surrogate this time around—in 1979 Santa Barbara.

They live in a big old house that’s being very slowly refurbished by one of their boarders, a vaguely hippie-ish fellow named William (Billy Crudup), a mild-mannered jack-of-all-trades. The other houseguest is Abbie (Greta Gerwig), a punkish photographer who’s into the local music clubs and, as we eventually learn, is a cancer survivor. A third young woman in Jamie’s life is his long-time friend Julie (Elle Fanning), two years his senior; she’s the daughter of a therapist whose mother compelled her to sit in with her patients in group, and frequently sneaks into Jamie’s room to spend the night in his bed—platonically, one must emphasize.

Dorothea, William, Abbie and Julie are all characters that have a distinctly literary feel, and they tend to act and speak in ways that come across as more than a mite precious on screen. (The same is true of William, who good-naturedly romances both Dorothea and Abbie.) What they all have in common, however, is that they circle around Jamie. Dorothea is a sort of seventies helicopter mom, who’s so deeply concerned about having her fatherless boy grow up to be a good person that she enlists everybody else to help in the effort. Theoretically a masculine presence should help, but realizing that William lives on a different wavelength, she appeals particularly to Abbie, who introduces the boy not just to the clubs but to the feminist texts she’s embraced. Julie pitches in as well, revealing the attitudes—particularly sexual ideas—that her background and reading have brought her to.

The result is that though Mills has created some fascinating female characters, the focus of his film is Jamie—that is, himself. That was the reality of “Beginners” as well, but in that case Plummer’s highly theatrical turn overshadowed McGregor’s recessive one; he really took the film over. Bening’s Dorothea is by far the strongest figure in this odd little universe, but nevertheless she is often pushed into the background for Zumann’s Jamie to take center stage, and though the young actor isn’t bad, his character is basically a rather fuzzy reactive vessel into which ideas and opinions are insinuated. It’s also the case that Dorothea, Abbie and Julie have to share the script’s attention in ways that Plummer’s Hal really didn’t; as a result none of them emerge with the sharpness they might have had, however fine they’re embodied by Bening, Gerwig and Fanning. Mills’ penchant for inserting narrative flash-forwards, in which we’re told what will happen to the characters in the future, seems an overly cute device to round them out. By the close the film feels fractured, a meandering collection of moments that, in the end, don’t fully cohere even if individually they’re engagingly laid-back.

Of course they are all designed to contribute to Mills’ larger vision about the passing of the era that has produced women like the three—though each comes from a distinctive background—who help to shape young Jamie. It’s hardly an accident that the story is set in 1979, at the edge of the Reagan presidency, and that one of the moments that the picture focuses on toward the close is Jimmy Carter’s “malaise” speech, which Dorothea finds inspiring while others around her are much less impressed by it. The spirit she (and to an extent, Abbie and Julie) represents will soon be replaced by something much less liberating and tolerant, more mundane and practically-oriented. One of the particular strengths of “20th Century Women” is that in pictorial terms it captures the end-of-the-seventies ambience so well, a testimony to Mills’ own obsessive attention to detail, but to the commitment of production designer Chris Jones, costumer Jennifer Johnson and cinematographer Sean Porter to his vision.

On the other hand, Mills gilds the lily with his more insistent visual touches—most notably long-distance shots of cars speeding along the coast that turn into psychedelically-colored rotoscopic images and collages of period stills and artwork—that are more reflective of advertising technique than traditional narrative method. Given all that, one must appreciate the skill of editor Leslie Jones in stitching it all together so well. The musical choices also contribute to the period feel—especially in Dorothea’s inability to appreciate the more cutting-edge sounds she’s introduced to.

The title of Mills’ film is more than a little over-expansive, given that it’s really about three rather peculiar females at a particular juncture of American history late in the twentieth century—or, more specifically, about a teenage boy growing up under their distinctive influence. It’s essentially an autobiographical coming-of-age movie, one that includes a good many affecting moments but, in the last analysis, doesn’t manage to bring them together into a satisfying whole.