I think it's the law on MN to be incredibly snotty about it. I hate those kind of films but what's with the competitive snottiness. Don't like it? Don't watch it! It doesn't make you superior for not liking it!
I think the snottiness - which I fully share, I admit - is in part down to Mamma Mia being hailed as some kind of great film for wimmin-y togetherness, where we all lie about in groups singing and being free-spirited and overdosing on wine and snacks in an unthreatening 'all girls together' way. It's promoted as 'what women want' from a film, and someone is out there right now trying to figure out how to replicate it at the box office.
I only like slow-moving French new wave films and screwball comedies, but I can usually see what other people like in more popular films, even if I don't like them myself eg The Shawshank Redemption has a feelgood ending, romcoms are good in that you can go and see one being pretty sure that no one will be violently murdered before the end of the credits, etc etc. I have to admit I can't with Mamma Mia. I genuinely don't get the appeal at all. The bits I've seen have the same effect on me as Great Auntie Nuala hitting the karaoke machine half-cut at a wedding.
Admittedly, I have never seen the whole film - who is actually the bride-to-be's father, or is that beside the point? And does she actually marry that annoying youth from The History Boys?