This movie basically lived up to my expectations and more. Director/Writer Joss Whedon (you may know him as the creator of Firefly) has done a fantastic job of knitting together a plethora of stand-alone heroes into one big live action film. This movie has it all: awesome action, great humor, witty Joss Whedon dialogue, and a decent storyline. Since I am not necessarily well-versed in the comic book universe, I cannot say how accurate this movie is to canon, but still if you love superheroes then you will love this movie. The only thing this movie really lacks in is romance I guess as well as a deeper symbolism/story as seen in Christopher Nolan's Batman movies.
I am pleased with the direction Joss Whedon has taken this franchise. The movie is basically a whole Avengers origin story, where all of our heroes are getting used to one another. It makes sense given all of the heroes come from diverse backgrounds and films of their own. Even more important, Whedon does not neglect the character development of any one hero. The balance is near perfect in my opinion. This movie is the start of something huge, a Marvel dynasty. I eagerly await the upcoming Avenger films, no doubt there will be more to come.
Pros well paced, great action, witty dialogue, logical story, balanced character development