The only negative aspect I could make about this flick is that it didn't last long enough. The pacing of this first ever Marvel team-up movie was so fast and fluid that it went through the 2 1/2 hours like it was merely minutes.
The story kept the dynamics of the characters interesting as no one, save for the exception of Banner & Stark, could get along. Stark & Rogers were at odds because neither approved of the way they handled their business, Thor felt everyone was tiny and weak compared to him and people had issues with the way Fury did business because he was not honest with him as to what he wanted the Tesseract for (cosmic cube for true believers).
And with Loki wielding a few tricks to have the team at odds with each other practically playing them like puppets.
Cast, except for Scarlett Johansson who played Black Widow, all turned in an excellent performance with Robert Downey Jnr stealing the show as the charismatic Tony Stark. That is the thing about Robert, he is able to steal a scene with his charm and personality even when it's supposed to be a team movie.
It's no surprise when Iron Man is considered to be the face of Marvel and for the movie franchise as well.
I was really impressed with the performance of Mark Ruffalo as Bruce Banner after having taken over from Edward Norton, whom I might add was unfairly dismissed from his role after the 2008 reboot of the Incredible Hulk.
But that said; Mark came in after already having the Hulk's story setup in this Cinematic universe and made the role his own with the awkward nervous demeanor that Banner showed. But that said if you had a 7" Green Goliath waiting beneath your surface knowing that he'd let out if you had a moment of anger, you'd be a little nervous as well.
The effects department went to Town taking into account the amount of visual effects that would be needed for Iron Man, The Hulk, the Scrolls (we know who they are) to help make the movie what it is.
They are Earth's Mightiest Heroes. And they proved that the Team-up formula for comic book movies can be done. DC. It's your turn.