To say that this is a "busy" film is an understatement. There are so many factions wanting to hurt or control each other that it made my head spin. The story is so complex I couldn't quite wrap my brain around it. It jumps between so many countries and and so many people that you need a map to keep up.
Does the film make sense? Not entirely. But it is a little more intelligent and definitely more entertaining than the average superhero movie. Just don't think too hard as you watch it; it will spoil the fun.
The movie should have been called "Avengers 3", because the movie is really about all the Avengers. I assume that the title has something to do with marketing.