It depends on where the Greeks are.
Greeks in the diaspora loved it. It is a movie that pokes caricatured fun at the antiquated notions that the first generation of migrants had, and how they did not assimilate and retained a rural worldview. That kind of caricature is a commonplace of second-generation members of diaspora when they get into comedy; it’s hardly unique to the Greek diaspora. (Compare for example the comedy done by the Indian and Pakistani diaspora in the UK.) Greeks in the US, Canada, and Australia were in on the joke, and they lapped it up.
Greeks in Greece and Cyprus… dunno, and I’d be interested to hear. What’s critical is that the worldview caricatured in the movie is a worldview that has long died out in Greece itself: the first generation of migrants remained in a 1950s rural timewarp. Greeks in Greece are likely to feel extremely detached from it: it’s not their modern-day reality, and its not their country. There’s that underlying truth at work, painful for anyone in the diaspora: those who left and those who stayed behind are no longer the same people.
For what it’s worth, the Greek title of the movie was Γάμος αλά Ελληνικά, “Wedding, Greek-Style”. It was a title reminiscent of the madcap comedies of the Greek comedy film industry of the ’50s and ’60s, and that was not a coincidence.
The most interesting reaction, which I monitored at the time, was that of emigre Greeks. I’m using the distinction between migrant and emigre Greeks on purpose: by the latter, I mean the much smaller, much better educated, affluent and urbane wave of Greek professionals who have moved to work in Western Europe and America over the last 20 or 30 years, as opposed to the peasants who moved to become factory fodder and small-businesspeople in the early to mid 20th century.
The two waves have very little in common, and don’t particularly associate. The clash has been most prominent in Canada, where the “emigres” are earlier, political dissidents from the ’70s, and in much greater numbers. The ’50s migrants and the ’70s migrants have formed separate community clubs: they can’t be in the same room with each other. There’s a wave of Greeks coming to Australia now, where Greeks are into their third generation (they are most of the waiters in Greektown, where I live). I’m not paying attention, but I’m sure there’s some cultural friction here too.
Anyway. I was subscribed to the HELLAS-L mailing list at the time, which was the mailing list for those emigres, in Greeklish: it was the main vehicle of Greek online until the Web became a mass presence in Greece and Cyprus.
Many of the emigres on the list were dripping with contempt for the film, and not a few of them demanded that it should have been called My Big Fat Greek-American Wedding. Because they wanted nothing to do with the hicks that film depicted. (I was gratified to see the main complainer being needled by someone else: “You’ve already been in the US for a decade; watch out you don’t get de-Hellenised yourself!”
The vehemence is because the film does not depict a reality the emigres have grown up with—but it does depict a reality they are adjacent to, living in America and Canada and Britain; so they couldn’t feel the same detachment I imagine Greeks in Greece would have experienced. It was more pressing for them to dissociate themselves from it.
Some of the threads on that mailing list are available here: Google Groups—provided you can read Greeklish.