The first half of the movie is just ok. It brings all the characters in, gives us a taste of the conflict coming (both within and without the party of superheroes), and sets up the plot.
Halfway through the movie, the heroes start arguing with each other, and it is just a non-stop, action-packed slam fest of epic greatness. Everything about it from that point on makes it into one of the best blockbusters of all time. Yes, I said one of the best blockbusters of all time. It has everything a great blockbuster needs: action, good looking people, enough story to compel you, and characters that you actually connect with.
But every time I watch it I come away with the same new life-altering mantra:
What would Captain America do?
Really though, just ask yourself that simple question and you will never go wrong in life.
I salute you, Capn'.