It was quite good, I thought—and the potential for this concept to become the most laughable garbage was huge! Not an easy bullet to dodge, I would think. Joss Whedon has a way of making me appreciate things that otherwise bore me SO badly, from vampire-slaying to comic book movies.
It probably helped that I had already seen the Thor and Captain America films—which were just “OK.” Those two characters have maximum potential to just seem incredibly silly, but with some back story I accepted them. Especially Captain America’s ridiculous outfit, like something from a musical stage show in the 40s! Well, that was explained in his earlier movie—it WAS something from a musical stage show in the 40s. And the character himself didn’t like that. Clever way to make the super-cheesy seem slightly less cheesy.
If I saw the Avengers cold without seeing any prequels, it could have seemed a bit cheesier... but no less fun. Even the action scenes (in other words, most of the movie!) were great, and I have little patience for the soulless action they churn out these days.
I even knew to stay to the very end and see both little added credits scenes.