Writer-director Sarah Polley's Away from Her was one of the very finest feature debuts of the 2000s, the sort of brilliant that makes it virtually impossible not to eagerly await everything she ever does in the future. Even when her follow-up is such a sophomore movie: not that Take This Waltz is at all a failure. God no, quite the opposite: it secures Polley's stature as a proper artist, freely moving through ideas and scenes that could only come from the mind of a filmmaker very confident in herself and her skills, and totally unafraid to tell a story the way it wants to be told and not the way that convention requires it to be told; it is a mess of the sort that only a brilliant person can slop up on there. It somewhat feels like she got the order of her movies wrong: Take This Waltz is the problematic, promising work of a creator who needs to find discipline to go with her insight, and Away from Her is the extraordinarily moving portrait of character of great nuance and sublimity, paying of the promise of her talent and proving that she has a masterpiece in her. Anyway, for all that Take This Waltz sometimes does not work - sometimes profoundly so - sometimes it works extravagantly well, and it manages to scrape out a performance of grown-up restraint from Seth Rogen that I would genuinely have assumed him impossible of giving, so that's a real achievement, anyway.

Moving from the long-married seniors of her first film to young people, Polley's script centers on Margot (Michelle Williams), who is just about up to her five-year anniversary of marriage to Lou (Rogen), and has long since passed out of the "we're young and in love and it's ecstatic" stage of the relationship, into the "we know each other very well and there's no surprises left, really" stage. This troubles her. What troubles her even more is that she has recently crossed paths with smoldering new neighbor Daniel (Luke Kirby), and though his brusque manner at first annoys her, in hardly any time at all she's busy making plans to accidentally catch a glimpse of him in the morning, and other similar behaviors that he playfully, and accurately, calls out as "stalking".

In the broad strokes, Take This Waltz is an exceptionally good, if unrelentingly dour depiction of the way that marriages deflate: while Margot is our one and only protagonist, Polley resolute does not take sides in depicting the reasons why the central relationship is suffering: Margot is emotionally unready to become a grown-up, with grown-up relationships that are about other things than intensity and chemistry, while Lou is satisfied and lazy and doesn't seem aware that any work exists to be done in maintaining his marriage, to say nothing of his willingness to do any of that work. They are, neither of them, particularly admirable people, and of course that's the point. Take This Waltz is about a couple unwilling to deal with the fact that their idealised visions of life are pragmatically impossible, and it is required of it that it have as little idealism itself as possible. Thus do Margot and Lou - and Daniel, for his part - all come across as particularly human-sized in their little pettiness and their fleshiness (this is one of those Michelle Williams movies where she's gone out of her way to look puffy and average, average as a gorgeous movie star can get, anyway). And this part of the movie works extremely well.

It's in the little details filling in the strokes that Polley starts to get herself in trouble, except when she doesn't; and that's the hell of the movie, that it swings from aggravating misjudgment to incisive perfection, sometimes in the span of just a few frames. At times, Take This Waltz feels uncommonly like a genre exercise, as though Polley decided that she wanted to take the most unbearably twee elements of the New Quirky Cinema, and suck them of all their hipster preciousness. It starts early, with a pointlessly complex coincidental meeting between Margot and Daniel at a historical re-enactment straight out of the Idiot's Guide to Indie Cinema, and as details accrue, it's unnerving how many of them are so cutesy that it burns: Dan's day job is a rickshaw, when he's not dreaming of being a painter; Lou is working on an all-chicken cookbook; Margot and Lou's panoply of couplish in-jokes have the extreme specificity of reality but the cloying humor of screenwriting. Having thus assembled a veritable army of quirky details, Polley proceeds to film them with a detached, airless severity that makes all of them seem even more foolish and trite. To what end? I have absolutely no damn idea, and it doesn't fail as such, though it seems like the director has made an awful lot of extra work for herself.

The film's real problems, though, aren't in its weird little dead-ends, or even in its giant ones (there's a significant subplot involving Lou's sister Geraldine, well-played by Sarah Silverman, that does absolutely nothing but take up space), but in its inconsistency. There are moments of brutal, cutting insight: an edgy scene riddled with jump-cuts in which Lou breaks down upon learning of Margot's emotional infidelity is one of the most potent scenes in any marriage drama I've seen in a long time, Rogen reaching heights implied by nothing else in his career; the awkward chemistry between Williams and Kirby in their pseudo-dating scenes is miracle of small physical acting. And their are clumsy gestures that fail: the hopelessly symbolic conversation about making connections... in the airport! that practically opens the film lays out the themes to come so baldly that you'd give it a failing grade in a film school screenwriting course. Polley and her actors also never seem to have decided on some fairly crucial questions about the nature of Margot and Lou's marriage in the five years prior to the movie: are we meant to see the last dying gasp of a relationship that ossified long before, or is all of this happening suddenly and violently (Rogen and William's interplay is on such a knife-edge between "easy familiarity" and "lazy boredom", and the film really needs to know which one it is).

The result is frustrating as only good movies can be frustrating: there's just enough that is true and brutal, with just enough nonsense getting in the way, that you can never decide if it's a flawed masterpiece or a generally unsuccessful work that keeps getting lucky. Polley and cinematographer Luc Montpellier don't help matters out with a visual palette that leans much too heavily on the sun-kissed and the over-saturated, resulting in a film that always looks slightly garish in a way that the material can't support; and while everyone in the cast is frequently great, Williams especially is visibly not challenging herself (this is so similar to, and so much less impressive than, her work in Blue Valentine, it's absurd), and Rogen frequently relaxes back to a more subdued version of his "I'm a dude" shtick, and Kirby frequently doesn't allow himself to reveal anything internal about Dan at all, just letting him be a tabula rasa for Margot. The characters, then, are not as well-defined as they could be; this fits in with the theme somewhat (it is a film about unformed people), but it's also a bit sloppy.

And then, on the other hand, we have things like the final shot, which is flawless, or the use of a lighthouse motif that evolves wonderfully over the course of the film. There's a hell of a movie in here, all right; I just wish Polley had spent a bit more time hunting for it.