If you want to understand the story better, read the novelization
I missed this film in theaters and ended up picking up the novelization. A few days ago I finally had a chance to watch the movie and I can say that, if you're confused by the story, read the novelization and it will be much clearer to you.
For instance, I see a lot of people saying, "WTF happened in DC?" Well, while the movie doesn't bother to explain it, while a good 60 pages in the novelization are dedicated to the DC battle.
There are a lot of other plot elements as well that are lost in the choppy editing and frantic pace of the movie, but that are made clear in the book.