This is precisely why Joss Whedon was the perfect choice for this movie. There is no one that is better at writing dysfunctional teams with the perfect amount of action, humor, tension, and drama. Joss Whedon stays true to form with this movie. There is the wise-cracker (Iron Man), the strong female (Black Widow), the mentor with the mysterious past (Nick Fury), the leader (Captain America), and the brain (Bruce Banner). The greatest thing about this movie is that Joss Whedon manages to make every character have any equally strong voice throughout the movie. There isn't a single "main" character. He even managed to make me like Thor, The Hulk, and Samuel L. Jackson as much as Iron Man and Scarlett Johansson.
And, of course, there's plenty of fan service throughout the movie in subtle ways. Famous lines are said in a slightly different manner, Stan Lee makes his appearance (I was the only one who laughed when he came on, so maybe I'm the only one in the audience who knew it was him?), and the after credits clip that sets up the next Avengers movie stars someone that I don't think many people recognize/know, but I was certainly excited.
I left the theater feeling super stoked and wanting to both watch the next Avengers movie and watch this one all over again. I don't think I can give it a higher recommendation than that...
The fact that I was in the very first row of the theater because I underestimated how busy the theater would be.
That Robin Scherbatsky was in the movie. She'll need to star in many other things before I don't see her as Robin.
Joss Whedon, the entire cast, Superheroes, every single part of this movie.