First of all, the pressure was huge. Getting so many strong characters into one story and having to do justice to them all was not an easy task. And they nailed it.
The movie had a great sense of humor, didn't take itself too seriously and still you felt there was something at stake. It also helped that the dialogs were so witty and clever and the actors obviously had fun with them too.
And then there was larger than life action, which is just so much more fun if you actually love the characters that are acting in it.
I'd even say it was the best popcorn blockbuster since ages.