It's in the nature of young filmmakers, if they have enough talent and chutzpah, to boldly go where (they think) no one else has gone before. Paul Thomas Anderson certainly has the chops, and in writing and directing "Magnolia" he's hung it all out, saying 'look at me! I can do it! I can do anything I want!' What he's done is make an amazingly good bad movie, a movie that fascinates and enthralls us from beginning to end, but a movie that, like a sand castle on the beach, starts falling apart as fast as he builds it up.

"Magnolia" is set in the San Fernando Valley, where we meet an Altman-like agglomeration of disparate people whom Anderson will pull together for us. The aging Earl Partridge (Jason Robards), a television mogul, is dying and cared for by his hospice nurse Phil (Philip Seymour Hoffman). A television host, Jimmy Gator (Philip Baker Hall), whose long-running children's quiz show is a Partridge Company production, is also dying. Both men have estranged adult children. Partridge's son is Frank T.J. Mackey (Tom Cruise), a men's sex guru (his seminar title is 'Seduce and Destroy'). Gator's daughter Claudia (Melora Walters) is now a cocaine addict.

We're only halfway there, because we also meet both the young quiz kid on Gator's show Stanley Spector (Jeremy Blackman) and a middle-aged former quiz kid now a washed-up failure, Donnie Smith (William T. Macy). And old man Partridge's young wife Linda is Julianne Moore, who had married him for his money but now as he dies has fallen in love with him. One more character completes the main list, and that is lonely cop Jim Kurring (John C. Reilly), who meets and falls in love with Claudia in the course of the film.

So what has Anderson done with this enormous plateful of characters? He's set them, and the film, in the course of a day, a day that begins in the California sunshine, goes cloudy in the afternoon, with rain coming as night falls, and turns into a torrential downpour that itself climaxes with a rain of frogs from heaven. You see what I mean about chutzpah. Almost every scene is a moment of drama or melodrama, a confrontation of one kind or another, as Anderson cuts back and forth from one to another in a collage that he intends to add up to more than the sum of its parts.

He has carefully begun his film with illustrations of the vagaries of fate -- how a building got its name from the names of three men who were hanged in front of it; how a man who leaped from a building to commit suicide was actually murdered on the way down when his mother fired a shotgun at his father, but missed and hit her son as his body passed their window.

What he wants us to see here is how chance rules much of life, but his film actually goes the other way. There are chance elements throughout, but they are far overridden by the deliberate actions of the characters. Robards asks his nurse to locate his son, and by dint of great perseverance he manages to do so. There is coincidence in that the Cruise character has just been forced by an interviewer (April Grace) to face the lies he's made up about his own life, so that we might say he's now prepared to face his father again, but timing, good or bad, isn't the driving force here.

What is the driving force seems more to be confession and its consequences. Gator confesses to his wife Rose (Melinda Dillon) that he's been unfaithful, but he won't admit that he molested his daughter Claudia. Claudia wants to confess to Jim the cop that she's a cocaine addict, but he keeps missing the signs. And yet Jim is like the force of truth in the film. He is without pretense and hubris. He prays to God but seems not to get an answer. And then he does. He does a good deed for Donnie Smith that he need never have done, and amid the rain of frogs comes the answer to his prayer.

The film is as richly textured as any in memory; the photography, by cinematographer Robert Elswit, captures each moment, each time of day, each location, each interior, each character, with his or her own quality of light and shadow. Songs by Aimee Mann spin throughout, including one magical-reality sequence where everyone in turn sings the same line: "It's not ... going to stop."

Where the film fails, and ultimately it does, is in the writing. There is simply not enough to his people beyond broad, almost cartoon strokes. Most of them are defined by externals rather than by some inner core. The exceptions are Claudia the addict and Jim the cop, who seem to be the only characters written from the inside out; and both Walters and Reilly seize upon them to give beautiful performances. Cruise here, playing a man who is all surface, struts and shimmers but is, oddly, without sex appeal. By refusing to seduce us he has somehow lost the power of his character, so that when he does come to face the man he hates he brings no power to the role. We just sit and watch, almost without interest. I would guess that the fault is Anderson's, for forcing Cruise to play against everything in his repertoire, and Cruise is not a deep enough actor to pull it off.

"Magnolia," though it fails to be the great American film it wants to be, is still achievement enough to be essential viewing.