"Is that a dent in Tony Stark's armour? Granted, Iron Man 2 was the second highest-grossing movie of the summer with a gross of $621M worldwide -- $312M of that in North America -- ... but globally that's only slightly more than the earnings of the original; and considering how well-liked 2008's Iron Man was, it wouldn't have surprised anyone if the followup had far surpassed its predecessor on the strength of good will alone."
Article author Kevin Williamson chalks this up to an Avengers-centric suplot which he felt was "shoehorned" into the story to tie things together. So his question is whether or not this will bode badly for unknown quantities like Thor and Captain America, not to mention The Avengers.
Williamson also has an interview with Robert Downey, Jr. in which the actor responds to the criticism: "I think it's amazing any movie gets made correctly at all because it's run by people and egos and personalities," he says. "The whole thing, it's a miracle to me that every movie doesn't suck. Avengers, it's such a huge idea -- how are we NOT going to screw it up?"
To wrap things up, the actor was asked how he felt about sharing screen time with other actors like Chris Evans, Chris Hemsworth, scarlett Johansson, Samuel L. Jackson and Mark Ruffalo, Downey quipped, "I feel like more time in the trailer."