My initial impression after watching this was that it seemed a bit too busy and unfocused. There were just too many avengers in this to make this a good stand alone movie.
The sub plot of the Avengers having to agree to a UN accord just seemed a bit contrived. It would have been more interesting to see the UN accord in effect and have a few scenes showing how it it effective and then later a scene showing how it gets strained somehow. Alas this is not how it ended up.