The only threat of the villains is Loki, who could be handled easily by Banner or Thor single-handedly. Barton and Banner were mind-controlled by Loki, but that was just temporary. Loki just started a war that he would never win.
The storytelling is highly unbalanced. The visual effects and action sequences of the last fourty minutes were sensational and thrilling, yet the long part before it was boring and useless. Some action scenes lack credibility and look fake, as nobody gets injured or bleeds, and the editing of the film is not convincing.
The name "Avengers" is misleading, since these superheroes are not avenging and are just saving the world. Particularly, the war criminal Loki was not sentenced to death. "Savers" might be a better name for the team.
Overall, this film does not live up to its hype.