2. He Doesn't Have Much of A Back Story
Mostly all the characters behave in accordance with their back stories; Captain America can't catch any references because the last time he was alive was in 1939; Iron Man can't accept being a hero because he's an egotistical, individualistic billionaire; and Bruce Banner can't get to hyped up, because he turns into a green beast that can throw helicopters. Hawkeye acts like a tough, isolated assassin; why? His story is not told directly: we can assume fragments of it through Black Widow and the fact that her past is interconnected with his. But we don't really know hers either, except that she was involved with Russians and keeps saying that she has some red in her ledger. Like we are briefly shown Captain America's past as he slams his fists into a punching-bag, Hawkeye and Black Widow's past need a little revisiting; hopefully we will see that in the next Avengers film, even with such a huge line-up of characters.