Well what can I say, A wonderful film, all the previous Marvel film's since 2008 have been leading to this, so you have all the main protagonists, Iron Man, Thor, Hulk, Captain America, throw in Black Widow (who was in Iron Man 2) and Clint Barton AKA Hawk-eye and what you have there is a mix of some of the baddest ass superheroes the Marvel Universe has to offer and then the guy who bring them all together Nick Fury, then you have the antagonist with Loki being a some what used villain still trying to step out of stepbrothers Thor's shadow.
All the characters blend beautifully each bringing their own uniqueness to the film, what also makes the heroes good is there is no pomposity to them they all have there flaws and this makes well more human, even though besides Thor they all are.
I am not really going to talk about the film cos no review could do this film justice, you NEED to see this.
With this film its ends what marvel call phase 1, I personally can not wait for phase 2 and the second Avengers.
Oh and please let Joss Whedon direct again the man knows what geeks want !