I agree that the laugh track was a little unnecessary. Also, Nick Fury was more a take on specific Samuel L. Jackson characters from other movies, more than actually Nick Fury himself. It felt like the jokes were only as relevant as you happened to know anything about the characters. The animation was decent, though. I didn't mind the Thor-explaining-his-return thing as much as the laugh track, for some reason.
I agree that Black Widow and Hawkeye (while I like them as characters in the books) hardly seem necessary the way the film makes it seem. The scene was a nice way to jab at it. As a big blockbuster movie? You could get away with having Captain America, as he'd be the guy with the most military experience and he's still just a jump to the left and a step to the right from being superhuman himself. But I can't really buy that in the Avengers, which are about combating threats so powerful that you can't send the SWAT team at them, would honestly scout by saying "The world is in need of the most powerful of heroes to defeat this new menace! Bring me a trick archer from the circus, and Xenia Onatopp or at least the closest analog!"
Silly.