I thought she was exceptional as Marilyn Monroe in Simon Curtis's My Week With Marilyn, but she's even more compelling in a far more difficult film, Sarah Polley's Take This Waltz, in which she plays a 28 year-old Toronto travel journalist who's been five years married to a perfectly nice and decent chicken cookbook writer and who finds her life turned inside out and upside down by a chance encounter with a struggling artist - who happens to live right across the road.
It's an irritating film in many ways because not a lot happens and it's mostly placed inside Michelle's head, as it were, as she juggles her affections, faces the fact that her life might be unravelling and yet somehow manages to finesse the crisis into a not too tragic resolution, rather like Celia Johnson in Brief Encounter.
Watching Williams on the screen is like watching a summer sky with endless white fluffy clouds scudding across it, occasionally laced with a threat of rain or thunder, but rearranging itself into a degree of composure at regular intervals while touched with a little dollop of experience.
Unlike stage acting, there is no physical gesture that sticks in the memory, no concerted physical action - apart from one extraordinary scene when she joins a crowd of women of all shapes and sizes in the communal shower room at the local gym. There's a rhapsodic sequence, too, on a fairground ride, and several almost embarrassingly intimate, though not explicit, bedroom scenes, and one other remarkable piece of writing where the handsome neighbour makes virtual love to her across a restaurant table.
It's all about acting for the camera, something Michelle Williams has been doing since childhood and then in a long run in the television series Dawson's Creek. How does this talent translate itself to the theatre? And does it matter if it doesn't?
Not at all, but I'd love to see this rare quality of utter emotional transparency and charm given a theatrical test in Shakespeare, Ibsen or Chekhov. But then again, maybe Williams feels that that kind of thing can be left to Carey Mulligan, whom in many ways she resembles. Either of them would make an ideal Viola in Twelfth Night; in fact, they could alternate as Viola and Sebastian and be the most sexually alluring and ideally gamine pairing in the entire stage history of the play.
An early evening outing to the cinema, even to a movie that, like Take This Waltz (the title is taken from a wonderful Leonard Cohen song that comes in towards the end), plays for nearly two hours, allows plenty of time for dinner.
And just around the corner from last night's screening was Brasserie Zedel, the latest venture of the redoubtable partnership of Chris Corbin and Jeremy King, by appointment to the kings and queens of theatreland. They brought you the Ivy, then the Wolseley, most recently the Delaunay... and now, the Brasserie Zedel, a big bustling French gastro-palace set in the magnificent gilded splendour of the old ballroom of the Regent Palace Hotel.
It's a terrific place for a treat, or an outing, but there are also places reserved for walk-in customers. And, here's the thing, it won't cost you an arm or a leg or anything like. It's fantastic value, and it's a slightly smartened up version of Les Halles or Chartier in Paris, with an authentic Parisian menu but without the severity of waiters in black tie and white aprons.
I've already spoken to a couple of theatre producers - Nick Allott, Arnold Crook - who say they virtually live in the place, though last night's crowd seemed to be a fair old mixture of tourists, theatregoers and suburbanites with not even a sniff of a Biggins.
Funnily enough, there's another new French restaurant in town, on the Old Brompton Road, that has also been receiving rave reviews, the Garnier, and I found myself standing outside its slightly forbidding exterior en route to the Finborough Theatre the other day.
But it's not the sort of place you'd go into on your own at six o'clock in the evening, though there was one brave couple perusing the menu by the front door. On that occasion I settled on a modest little Italian place round the corner. The Garnier is for your first date, perhaps, with Michelle Williams. The Brasserie Zedel is for absolutely any time you feel like it.