Saw it Friday night, loved every minute of it. I was a bit weary at first, thinking it was gonna be too cramped with the large cast, but it wasn't. They made the large cast work wonderfully! It did get a tad confusing at times, especially near the end with all the action seeming kind of all over the place, but it was still solid. One extremely notable improvement over the first one is that it gives all the main characters actual roles instead of characters like Hawkeye simply being there to kill some people. It also did a good job of setting up Civil War with Cap and Iron Man having their disagreements and Cap forming what I imagine is going to end up being his team in the aforementioned upcoming movie. A fantastic movie overall.
One thing that disappointed me, though, is the fact that Quicksilver died. Yes, I agree somebody had to die, but Quicksilver was the wrong choice imo. He was just introduced in this movie and his story was far from complete, so I wasn't hit very hard by his death. Plus, he didn't need to die. He shouldn't have sacrificed himself to save Hawkeye, especially since Hawkeye tried to kill him several times in the movie, including only a few minutes earlier. Still, though, I'm glad Marvel finally got the guts to kill off a main character, because they have a bad history with "killing" characters (*ahem* Phil Coulson, Nick Fury, Captain America, Loki, Bucky Barnes, JARVIS, Pepper Potts, among many others). Minor point, and it doesn't really drop the quality of the movie much.