The plot is pretty banal. Kym comes home from rehab for her sister's wedding. Kym is a self-absorbed nightmare. Weddings are somewhat nightmarish in and of themselves. But they're also supposed to be joyful happy times, and, big surprise, this one is too. The process of everyone in the movie coming to terms with the premises and gradually becoming better people isn't nearly as ham-fisted as it tends to be in such things. And the movie certainly is remarkable in portraying its characters in a deeply sympathetic way, but without shrinking in the slightest from their faults. They appear at their best and their worst, and you may not like them very much, but at very least they're pretty realistic. Well, maybe slightly on the saintly side - personally, I would've let Kym have it a lot earlier in the film, but hey.
I think what's most interesting to me about the movie is the way that early on, there's this really elegant juxtaposition of two scenarios - an AA meeting and a wedding rehearsal dinner, or more specifically, a series of wedding toasts. I loved this, because it very subtly points to how similar they are. Both are situations in which people are called upon to stand up in front of a large group and relate somewhat humiliating things about themselves and/or others. But, because it's a socially sanctioned thing, nobody is actually really appalled or offended by the related events, and people are, for the most part, not actually ashamed to relate them. The similarities are striking, but then - and this is kind of brilliant - Kym delivers a toast that adhere more to the conventions of AA than to that of a wedding, and you realize the difference. Weddings are all about the people getting married - AA is all about you. A somewhat trivial conclusion, but the process of getting to it - for me at least - was quite interesting.
But that's the thing about the movie - scenes like those described above are conceptually interesting, but not much fun to watch. Boring at best, cringe-inducing at worst, it just doesn't make for entertaining screen time.
There's another interesting aspect to the film that I haven't really thought about much, namely, the wedding itself. Some friends of mine found it obnoxious in its insistently interracial, intercultural, so-liberal-it-hurts-ness, whereas A O Scott, in his review, seems to suggest that its utopian aspects are part of a delicate balancing act in the film between joy and despair, sentimentality and melodrama. He points out that, for all its seeming naivete about cultural division, it comes across as remarkably realistic, which is true. Which isn't to say that I loved it - I really appreciated that the interracial aspect wasn't that big of a deal, but the whole smorgasbord of cultural traditions wedding was kind of annoying. But it's an interesting aspect of the movie that deserves more thought.
So ultimately, is it a good movie? Yes. Do I recommend it? Kind of?