The way I see it is people have been going out to see the Marvel movies over the last few years. And they have been going in large numbers.
If you have seen more than one, you've seen that these films have been building up to The Avengers.
If someone has seen more than one Marvel film recently, they will most likely be going to see the Avengers.
So suck or not, Avengers will have a killer opening weekend. After that, the strength of the story will matter. But the film will have made it's tens of millions by the.