It seems to me that the biggest issue most people seem to take with Iron Man 2 is the involvement of two very distinguished SHIELD agents (Nick Fury and Black Widow) and how that involvement is much akin to a high-jacking. They even go so far as to place Tony under house arrest during an extremely pivotal moment in his life. But this is what SHIELD usually does in the comics - they get in the way of things, so my gripe isn't how they interfered, it's more along the lines of WHY they are there in the first place.
 
When you saw the first film and learned of SHIELD's existence in the Marvel movie-verse, I bet you were a bit skeptical, considering the base of operations is on a giant floating aicraft carrier known as the Hellicarrier, the grounds for a semi-realistic presentation just couldn't have been available, although perhaps Tony will be the one who develops the power source to maintain that much flight (since Forge and Reed are Fox properties). At any rate, even with expectations generally low, I found just about every aspect of SHIELD in Iron Man 2 to be a huge disappointment. Nothing seemed to fit right.  

First comes the aesthetic...
You have Nick Fury walking around an exceptionally hot Los Angeles in a big black leather trench coat, and less than a minute later, Black Widow is seen wearing a SHIELD (navy blue with grey straps) variation of her trademark catsuit - in a diner. On that note, the SHIELD Black Widow suit seems more like a uniform, except she is the ONLY person who wears it. Granted, Samuel L. Jackson might look a little strange in a matching skin-tight outfit, but in that case, why bother smacking the SHIELD logo on the shoulder? 
Then comes the personality.... 
It ONLY makes sense that Nick Fury be present as the director of SHIELD. There have only been three different directors to my knowledge - Fury, Stark, and Hill. That seemed pretty easy to get right. Except that there are only three SHIELD agents with names, one of which, didn't exist in the comics until now. Are they really having that hard of a time finding recruits? In the 616 and Ultimate continuity, yes, Black Widow is a SHIELD agent, although she really wasn't a part of the team before the program got off the ground, pun intended. I think it would have made much more sense to have at least two additional SHIELD personalities, like GW Bridge and Dum Dum Dugan, who both have a lengthy history with Nick Fury AND SHIELD. I understand why Black Widow would be used in place of Contessa Valentina Allegra de Fontaine, although there is a bit of irony here. See a lot of people speculated that Black Widow was to be used in connection with the Crimson Dynamo, as the two share a troubled Soviet history, but for the sake of nationalities, Marc Scarlotti and the Contessa are both Italian. Do you agree?
And then comes the meaning....
So why is SHIELD there? Seems to be they want to keep a watchful eye on Stark, in what seemed like a tease for an Armor Wars theft, but only truly so that they could assess whether or not he'd make a good guitarist for Fury's superhero band (yes, I liked that joke). For the sake of the story at hand, SHIELD was involved to get Tony back on his feet, which seems awfully altruistic for a shadowy organization of their alleged caliber. Testing the waters is what I think it came down to. In Iron Man we see the combined efforts of three superheroes (Iron Man, War Machine, and Black Widow) taking down what Tony refers to as a "Hammeroid attack". Each of the three had an instrumental part in that effort befitting of their talents, and while it did indeed work, I think a lot of people were looking to see IRON MAN kicking ass, not just taking his slice of the action. Be that as it may, if you were looking for anything to convince you that the Avengers movie could work, you got that glimpse in the last action scene of Iron Man 2.
 
What do you think? Will SHIELD evolve into something greater than a couple suits on hand? Will we ever see the Helicarrier, and if so, would you want it to be used as a gigantic 1984 metaphor? Will SHIELD serve as an allegory for the big American government, or will it spread across continents as an international organization? Lastly, will the Avengers be more than glorified SHIELD agents?

Why can't SHIELD keep a Helicarrier? They keep BLOWING THEM UP. Geez guys,make the thing out of Adamantium and Vibranium,and self repairing nanites and irradiate with cosmic rays,and have Galactus as head of security!