I liked the Avengers as much as the next guy. There's no denying or minimizing the significance of finally seeing several solo-movie superheroes on-screen together for the first time. I was especially impressed by Mark Ruffalo's portrayal of the Hulk (both alter egos, though his action scenes were marvelous). However, I feel that the film also exemplifies a certain problem with the MCU as a whole: small world syndrome.
In his effort to make the Marvel Cinematic Universe self-contained, Joss Whedon has effectively cut out the human element of the Avengers in order to insert the plot machine that is SHIELD.
Hank Pym and Janet van Dyne were essential to the Avengers in the comics (Jan even named the team, in the beginning), and helped form a core that allowed the team to endure beyond cataclysmic situations. In the comics, the Avengers are friends that trust in each other, and Janet (often singlehandedly) facilitates that trust.
Janet's presence in the first Avengers film was cut, and now it looks as if Hank Pym's equally important role in Age of Ultron will either be minimized or cut entirely. I feel like Joss Whedon doesn't like these guys, though he seems to like a bunch of other things, among them the Maximoffs, abrasive personalities, and the Millaresque interpretation of how an Avenger operates: angry, cynical, and subservient to SHIELD, regardless of its immorality.*
SHIELD is the shoddy Superglue that holds the MCU together. The heroes that comprise the Avengers should be banding together based on something other than the intent of this organization, perhaps their own rapports with the other characters, or a basic ability to recognize world-ending threats and their abilities to stop them. Most of all the MCU should feel big. Instead, it feels cramped, as Nick Fury and the creative teams both literally and figuratively stuff the entire cast under one roof.
*Yes, several of the characters confront the somehow-irreproachable Fury with their knowledge of his plans to make new and more dangerous weapons, but:
1. The characters all ignore the larger implications of this, as they are apparently unable to conceive the possibility that a shadowy, faceless organization run by liars may not have humanity's best interests in mind.
2. Fury is utterly off the hook by the end of the movie (it happens again in Winter Soldier).