Given that this is a film for women and all that comes with that, it still doesn't work very well. It tries hard to be enjoyable and not overly sentimental, but it fails in several major ways that make it rather hard to watch.
The writing is a huge problem, as it's just not consistently very good. In fact, the movie is split into two seperate cases. In one half, there's the comedy, which works fairly well; in the other half, there's the dramatic aspect which constantly fails on every level. It doesn't help that Katherine Heigl's character is a milquetoast sop at every turn and puts up with bullshit from everyone, most particularly her cunt sister. And we're supposed to come along for the ride for far too long.
Heigl herself actually keeps us onboard for much longer than we should have, because she is an enjoyable actress and her big round eyes are more expressive than most of the rest of the movie's actors. The only other performance that works is James Marsden, killing his role and coming out of the film as the only actor unscathed by bullshit.
You're never exactly sure if you're supposed to side with the sappy, feminine view of the wedding as bullshit fantasy story or Marsden's view of the oppressive wedding industry bilking women and providing nothing but fluff instead of realistic marital expectations. The whole argument is lost over the film's course and it becomes Heigl's struggle to come to terms with her own life as a sap who gets trod on.
Sadly, that doesn't leave much, as only when the thorny Heigl and smug Marsden are scraping against each other does the movie provide any wit.