I'm not an ABBA fan, but I enjoyed it tremendously.
I consider it to be the theatrical equivalent of films like "Road Trip" and "Porky's" and "Harold and Kumar Go To White Castle". Films that fly under the radar of any intelligence and sophistication that you may have and entertain the stupidest part of your brain. And once the stupid part of your brain starts laughing, the intelligent part starts laughing too.
The thing that gets me about "Mamma Mia" is that there is no dramatic tension to it. As soon as the three men show up, you can figure out who is going to end up with who.
The only dramatic tension in it is when you see them pull on the rowboat named "Waterloo" and realize "Hey, I haven't heard 'Waterloo', yet? When are they going to sing that?"
And, too keep that slight thread of tension going, they don't sing it until curtain call.
"A coherent existance after so many years of muddle" - Desiree' Armfelt, A Little Night Music
"Life keeps happening everyday, Say Yes" - 70, Girls, 70
"Life is what you do while you're waiting to die" - Zorba