Joy is weird as all hell. The film makes many false steps, both in its screenplay and its direction (both by David O. Russell, though it is fairly well-attested that the back half - the much better half, as it happens - has been changed far less from Annie Mumolo's original draft), with a terrifically impressive-on-paper cast marching fearlessly into some very indefensible decisions. Decisions motivated by the utter screwiness of the script, I should point out, which for its first 40 minutes or so paints a portrait of human domesticity that's somewhere between a Chuck Lorre sitcom and a Luis Buñuel explosion of the moral behavior within families. It is as close to completely dysfunctional and at times acutely unpleasant as any 2015 film that still turns out to be kind of essential viewing. This is a really weird film; weird in the ways that make something captivating no matter whether it is "good" or not.

Fighting to redeem the film, frequently as the only salvageable component of the filmmaking process, onscreen or off, is Jennifer Lawrence, making her third film with her new artistic life partner Russell, but only the first of those where she's the clear-cut solo lead. Two things immediately suggest themselves: one is that, yet again, Russell has stranded the actor in a role that she's visibly much too young to possibly carry off, though it's far less obviously the case here than it was in American Hustle, so let's not dwell on it. Because the other thing is that this is the first time since Winter's Bone way over at the beginning of her meteoric career that Lawrence has been really and truly great in a movie. This is a star vehicle of the most ancient stripe: not so much a film which Lawrence, by dint of her acting skills, performs an act of lifesaving triage upon (though that does happen), as a film which primarily exists so that Lawrence can demonstrate that she has those skills

The weird part is that for all it's absolutely clear that Joy is only first and ever a parade of scenes that let Lawrence showcase her range, from weepy existential suffering, to batty, frazzled comedy, to Terminator-style severity and mercilessness, it's equally absolutely clear that this is an ensemble piece, the heir to Russell's early neo-screwballs Flirting with Disaster (still, to my tastes, his best movie) and I ♥ Huckabees in that, like those films, it assembles a whirlwind of weird grotesques and smashes them together to see what happens when equally exaggerated but tonally opposite caricatures are forced to interact. Frankly, I don't have a goddamned clue what to make of it all, but transforming an ensemble farce into a star-led dramedy (or, more likely, heightening the ensemble elements of a primarily solitary vehicle) makes Joy at least unlike most other films out there. For long patches in the first half, Lawrence is the only thing about the film that works, but at least it has the benefit of being utterly abnormal in its failures.

The film is, in a very noncommittal way, the story of Joy Mangano, a single mother using herculean force of will to keep her family orbiting around some kind of gravitational center, en route to inventing the Miracle Mop and becoming a millionaire entrepreneur and inventor of sensible household goods. Stand all the way back, and it looks like a thoroughly conventional biopic, which is, to be fair, what it largely becomes right around the time that Joy (never given a surname in the film) appears in the flesh on QVC, the television station where she hawked all of her early successes. And it is weird that the exact moment that it falls in line with one of the most tedious of all genres that Joy starts to become worthy of its leading performance. The QVC scene is, in isolation, one of the great pieces of thriller filmmaking in 2015: Lawrence stands on the empty TV kitchen set with a completely empty expression, while offstage QVC exec Neil Walker (Bradley Cooper, giving the only performance other than Lawrence's that can be confidently described as "very good", albeit with only a few scenes to take care of) hisses and frets and panics. Russell and his editors let the moment stretch and stretch and grow increasingly awful, until Lawrence starts to boot up like an ancient computer, and then snap into place quite suddenly, with the burly confidence she's embodied all through the movie. And from here on out, the movie is mostly smooth sailing, mostly: it moves at a crisper clip, and Joy becomes more than a series of variations of "I'm poor and you're stupid", which means that Lawrence doesn't have to fight as hard to drag meaning out of the movie.

Until that point, whatever are we to do with Joy? It is a carnival of terrible, stillborn characters. There's Joy's snappy grandma Mimi (Diane Ladd), tasked with the unenviable job of reciting the gloppy aphorisms that make up the film's narration; Robert De Niro is up to his usual late-career trick of being snoozy and monotonous as Joy's hapless dad, forced to rely upon his daughter's largesse after his latest marriage collapses; Isabella Rossellini dives unapologetically into camp as his new girlfriend. Virginia Madsen is trapped in the shrill cartoon of Joy's agoraphobic mother, communicating with the world only through references to her beloved soap opera. Joy's ex-husband and father of her two children, Tony (Édgar Ramírez), living in her basement, is the surprising source of relative sanity and stability in her life; best friend Jackie (Dascha Polanco) is another. Having other recognisable grown-ups besides Joy in the film helps, but only a little; this is still a fluctuating system of cartoons, some more cartoonish than others, but few objectively human (there's never a point where Rossellini's Trudy feels like anything but an addle-minded gorgon, even when the rest of the movie has generally picked itself up).

Watching Lawrence's iron-willed Joy cut against that is galvanising, enough to make one wonder if that was Russell's strategy all along. If so, it was a tremendous miscalculation, for the opening of the film isn't so much watching the Last Sane Woman hold her own in a warped world, but rather more like drowning until Lawrence comes along to take pity on us. She's great, well and truly; probably not "top five of the year" great, certainly not in a year with as many sterling female leads as 2015 has boasted. But Joy presents her to the best effect that anything ever has in her short career as a superstar: this is all of Lawrence's strengths magnified and all of her weaknesses (brittle irony that stands in for humor; a rather persistent interpersonal chilliness, which is weird given how goofy and beguiling the actor is in her public appearances) turned into character details and thus made merits. It's a fascinatingly dysfunctional star vehicle, but given its apparent goals, a successful one.