I rented Mamma Mia from Netflix this week. I only made it through the first 30 minutes. It is the first movie since Batman and Robin that I just gave up on. It was just so silly; stupid really. I cringed to see Meryl Streep acting like a total idiot.
My sister bought the DVD for my father, who is a total Meryl Streep fan. He couldn't watch it. I thought maybe it was because it was a chick flick so I decided to try it myself. Nope, Pa was right, it is just a bad, embarrassingly bad, movie.
It reminded me of the film of the musical, The Producers. People who should have known better translated the play's broad comedy to the movie screen unmodified, pushing things so far over the top it was like a fountain of stupidity. You do need to tone things down a bit when you are making a movie.
This is my own opinion of course. Yours may vary.