To say MOS wasn´t good just because not everybody liked it is the same thing as saying Sushi isn´t good, because many people don´t like, and pizza(The Avengers) is much better because most people like it. Some movies simply have more controversial elements than others, wich makes it difficult to please everybody. Some movies have a more friendly structure, wich makes it easier to please the masses. Not everything is for everyone, and i see no problem in having something that simply isn´t everybody´s cup of tea.
I love the Human Centipede. Both movies. But they got horrible reviews. Does it mean they´re bad horror movies? I think it simply means they´re too much for most people. Most people just feel disgusted by watching it. Wich means, this movie isn´t for everybody.
MOS doesn´t have the most friendly structure in the world wich makes it a good target for complaints. But i´m pretty sure that if Zack Snyder wanted to have no controversy surrounding his movie, he would have make it way more lighter, without Superman killing anyone, with less destruction, with more comedy and more romance. But he chose to make the Superman movie he wanted to see instead of the Superman movie that would have pleased everybody.
The Avengers is a movie developed to please everyone and to create no controversy. And you can see it in the way it handles itself. Everything is light, everything is bright, everyone is happy and beautiful, everyone has style, the heroes don´t kill anyone in a violent way, every line has a joke, the characters are always trying to be funny, yada, yada, yada. It´s too obvious that this is highly aimed at kids and families. This is a "feel good" movie. It´s a movie that´s afraid to piss anyone off. It´s too safe and very similar to watching a sunday morning cartoon.