Note: this is a reply to Maria Aspan's discussion of the four key things that worked about the Avengers (at movieline.com).
Re: The Avengers doesn't try to give equal time to each of the heroes; it might as well be called Iron Man 2.5. Thor is there to swing his hammer and drop off the villain from his movie, Hawkeye gets brainwashed before we even know him, and Captain America fades into Tony Stark's straight man. And you know what? Those are good things. The movie's already over two hours. And by choosing a few Avengers to focus on, Whedon made me more invested in what happened to Stark and Black Widow and the Hulk during the course of the movie.
Stephanie Zacharek, you'll note, saw it different. She argued that Iron Man's pronouncement, his "self-important wisecracks, begin to wear a rut in the movie" -- that he wore on us, leaving the hero who all along didn't try to hard -- Captain America -- as the stand-out Avenger. She said it was the hero who remained most human that you remember; and it is true that the ground fight involving the least powerful Avengers -- Hawk Eye, Captain America, Black Widow -- left together enough human precariousness and human uplift to make them seem for a moment the human core and the rest as external battle armaments. I wrote awhile ago, in a comment that may, alas, have gotten lost in the woods, that we might see in this film a transitioning away from the super-hero types we've gotten used to wanting to associate with -- the wise-cracking Wolverine or Iron Man types -- towards actually wanting the patriotic, the square, the straight-man types redeemed for our appreciation, even our identification. I thought the old preference would have to be allayed, played to, to make the transition possible while keeping our self-respect. I think we're all still more here with Iron Man than we are with Captain America, as you argue, but that comment in the film about America actually being in the mood for old school, and the scene where Captain America garners the respect of the police force, began to clear a path, I think, for Captain America to more take over in the next film -- with his perhaps even being accorded a knock-out win in an argument with Stark, with average intelligence but solid virtue stearing wit and snark clear to the side. How this will happen while engaging an inter-galactic villain, I don't know, but I still expect to see it.
A final note on this: there was a sense when Iron Man brandied wits and, well, brandy with Loki, of these two actually being co-sympathetic, fundamentally akin -- with both being conniving, smart-as-sin, full-of-themselves court wits, who'll ultimately need to oblige themselves to more straight-laced kings. You're right -- Iron Man's sacrifice didn't register (note: I'm referring here to another of Aspan's comments; specifically that she "believed in Coulson's death much more than the movie ever made [her] believe that Iron Man would actually have to sacrifice himself to save Manhattan); and, we noted, it was the best that he had. Penny is going to need to absolve him, and perhaps with this, absorb him -- already she wasn't seeming so second-fiddle; instead as if already reeling in the stray dog wanting his being reigned in.