The Final Shot:
New York has been trashed, but the Avengers have prevailed.
In a gorgeous final shot, we're told that Tony Stark (Robert Downey Jr) has learned how to become a team player, and is possibly even more committed to the Avengers than ever.
How are we told that? Well, the STARK sign on the top of his building has been beaten up, just leaving a single 'A'...
If It Had Been The Opening Shot:
It would have had a different meaning - A for a-hole maybe, because that's what most of the Avengers think Stark is.