Marriage, says the cynical journalist played by James Marsden in Anne Fletcher’s romcom, is the last form of slavery. 27 Dresses, however, contradicts this statement at every turn. It is what you might, if you want to irritate your female friends, call a women’s film, or perhaps a date movie. It would be best described, however, as thoroughly dated.

Not that there is necessarily anything wrong with that: think of the romcoms of yesteryear and the stars who shone in them. Even so, there is absolutely nothing to distinguish 27 Dresses from very average fare, unless it is the playing of Katherine Heigl as our confused and confusing heroine.

She is a fresh face on the scene, heralded after Knocked Up as something special, and plays here with a natural grace and a modesty that makes you almost believe in her slightly silly character. She could become the new Reese Witherspoon, but she’ll need better parts than this one, written by Aline Brosh McKenna (who also adapted The Devil Wears Prada for cinema).

Heigl plays Jane, a wedding enthusiast, always the bridesmaid never the bride, who loves helping worried brides with their outfits and even the cake, and rushes from one set of nuptials to another to watch the happy bride-groom’s face as he approaches the altar.

When she has more than one to go to on the same day, she engages a cab driver to ferry her all over New York — she has to change her dress before each wedding in the back of the taxi and every time the driver peeks in his mirror she docks him $20. There’s not much left for him by the end.

But sex hardly figures in this slightly gooey film because, like the heroine of an old movie, the virginal Jane secretly hopes that one day her own true love will come knocking. However, that doesn’t seem likely since her boss at the advertising agency where she works (Edward Burns) doesn’t return her longing looks and prefers her slut of a sister (Malin Akerman).

When he finally kisses her, after she’s deliberately wrecked the announcement of his impending marriage to her sister, she knows it doesn’t feel quite right. Meanwhile, her best friend (Judy Greer), who sleeps around like her sister, despairs of Jane ever summoning up the courage to declare herself to anybody.

All this is before she meets Kevin Doyle (James Marsden), the writer of the New York Journal’s marriage column, who is fascinated by her strange love of the wedding ceremony and has the temerity to write a piece about her without her knowledge. When his feature, about her and her 27 bridesmaid dresses, reaches the front page of the style section, any possible romance between them seems impossible. But, wouldn’t you know it, there’s a way out…

Marsden, who appeared in X-Men and Superman Returns, seems relieved to be in a movie in which his character isn’t competing with CG effects. But this is really Heigl’s film, since she often manages to make the most obvious of dramatic devices seem a little better than they are. The moment when the pair get a bit drunk and sing Elton John’s Bennie and the Jets as they dance on the counter of a crowded bar shows what they can do together.

But this is far tamer than Knocked Up, too determined not to undermine our tenderer feelings about weddings and marriage while pretending to be ironic about the whole fraught process. Which is what gives the film a saccharine quality that even Heigl can’t overcome, as hard as she tries. Still, the 27 dresses are fun and everyone likes to remember weddings, even ghastly ones.