If I’m reading the tea leaves correctly, Marvel Studios is going to do a very clever thing, and make movies within the same universe, BUT not make all of them be straight up superhero movies, per se. Guardians of the Galaxy looks like it’s going to be a looser comedy/action piece. If Black Widow gets here own movie, it will probably be closer to a Jason Bourne movie than anything else.
So while it will tie in to the Avengers and be consistent in terms of canon, it doesn’t have to be stylistically consistent.