Throughout the film, Black Widow (Scarlett Johansson) is presented as intelligent, cunning, resourceful, physically powerful and well-trained in the various arts of armed and unarmed combat. But none of this is ever emphasized. None of this is ever celebrated or highlighted. At no point does anyone express shock that Widow can kick a certain amount of ass. At no point does anyone question whether she can or will be brave enough to handle herself during the climactic battle. When she does her various (no spoilers) heroics, she does it purely because she's the only one who isn't otherwise distracted and it has to be done. Yes, she wears a form fitting outfit, but at no point does anyone comment on that, be it through dialogue or suggestive leering. None of the male Avengers try to hit on her, nor do any of them feel the need to push her out of the way of danger (and, unlike most films involving a token tough chick, she doesn't get wounded during the finale and taken out of commission). In short, she is treated not like 'one of the boys', but as an equal member of the team. Again, this is simply accepted as just the way things are.
I reiterate this point because A) I've always said that social progress comes when you don't have to make a big deal about it and B) a recent study shows from Social Psychological and Personality Science I'm correct. In short, efforts to 'feminize' role models in the areas of science, technology, engineering and mathematics actually reduced girls' interest in those fields. Attempting to attract female interest in what are now somewhat male-dominated fields by showing theoretical female scientists or mathematicians who were dressed in pink, wore conventional make-up and expressed interest in fashion magazines made young girls less interested than would-be female role models who just dressed like everybody else and just happened to be women pursuing said educational/career pursuits. So basically, condescending to young girls, while also promoting gender-specific stereotypes was less helpful than merely showing off successful scientists and/or engineers who just happened to be women. In other words, drawing attention to gender stereotypes in-fact perpetuated and encouraged gender-role bias. I know, you'd think that would be a no-brainer.
Tens of millions of young women will likely see The Avengers this summer in America alone, let alone the countless millions who will see it worldwide. They will be seeing a story where the idea of an extra-capable female superhero, one who is neither sexualized nor defined by a love interest, is so un-noteworthy that it doesn't even warrant acknowledgment. And while The Avengers 2 could use a few more female characters (and/or minorities too), the female representation on display is the very best kind. The women in The Avengers are absolutely equals to the respective men in their fields, and Whedon knows that this is not something that needs to be noted or explained. That Black Widow is as capable as the (to be fair, non-super powered) heroes is a given, because otherwise she wouldn't be there. That the various female SHIELD agents are there purely because they are good at their jobs is a given, because otherwise they wouldn't be under Fury's command. In that specific sense, showing off female equality and making it seem like no-big-deal, The Avengers is probably the most feminist film you'll see all summer.