First of all, we’re not even going back in time to peek behind the scenes at any of Marilyn Monroe’s major movies. We’re not tagging along with her during the shooting of the comedy classic “Some Like It Hot,” or during “The Seven-Year Itch” or “Niagara” or “All About Eve.” “My Week With Marilyn” is a buttermilk tale of adolescent lust and adulation that neither matures nor becomes interestingly curdled by the end of the movie or the end of shooting “The Prince and the Showgirl,” a movie about charmed people’s dalliances that might be most impressive for how dull and ugly it is, despite its royal trappings.

But that’s not the first thing you’re liable to notice when watching “My Week With Marilyn” (based on the memoir by an uncredited third assistant director for whom this week was the fodder for the rest of his life’s dreams and cocktail conversation – out of necessity since his only other film credit, ever, was working sound on a TV series in 1974). The first thing you notice is going to be Michelle Williams. You’ll be craning your neck for her like a fan. And when she arrives, you might not be transported. You might just be underwhelmed.

There’s a hardness in her eyes, and it looked, to me, like the pain of someone who has seen a loved one disappear into a rabbit hole of drugs — but will never give themselves up to that fate. Her Marilyn navigates the lonely, lavish logistics of shooting the English movie like a well tended ping pong ball. On set, she flubs her lines and becomes increasingly frustrated by her beauty-given power. She’s not dumb, but she is so hard on herself it frequently stupefies her, and brings the knives out from everyone else. Not that knives are needed when she’s throwing so many pills down her throat, but hey.

Although you might be willing to pin it all on Williams’ so-close-and-yet-so-far performance, the whole feel of the movie is a bit strange. It might be because director Simon Curtis and writer Adrian Hodges have been doing primarily TV movies for the last 20 years. It might be because Kenneth Branagh, as Laurence Olivier, is upstaged by Williams’ weak performance, or because Emma Watson, the best thing about Harry Potter, took a role as a one-dimensional costume girl with the sexy confidence of a “Peanuts” character and still is more likeable than Marilyn, or because Julia Ormond plays Vivien Leigh (Scarlett freaking O’Hara!) with an uninterested, dry-eyed, crusty disdain.

It might be because I’m still rooting for Eddie Redmayne, who already played the kind of smitten, dewy-eyed young man who will never have enough chutzpah to grab a girl and just kiss her in 2009’s dreadful “Powder Blue,” I still think he has tremendous talent that, so far, has been wasted on playing pent-up good boy parts.

But Williams? She’s not Marilyn. You might say that no one could be, but look at Robert Downey Jr. disappearing into Charlie Chaplin. Look at Gary Busey reincarnating Buddy Holly. It feels like Chaplin might be still living among us, on his 10th wife, re-inventing comedy, or that tonight is actually Buddy Holly’s last show, and we can still catch it if we run.

Not so with Williams’ performance. She just makes you feel like she’s playing a too-cautionary tale, but has never been — and will never be — in danger of going over the edge. Marilyn was always that way, it seemed. But that doesn’t make her un-reproduceable. It’s not that you can’t totally and believably and heart-wrenchingly embody and bring back to life an iconic person. It’s just that “My Week With Marilyn,” well, doesn’t.

Ashley O’Dell reviews movies that aren’t in theaters anymore. Except for this one, because her godmothers took her out for sushi and a show in Tucson.