I feel like Iron Man 2 got caught in the "leave breadcrumbs for future movies and make it all connect" issue. War Machine, Black widow introduced, Hammer was brought in clearly to be another big bad (and it didn't stick)
i still liked it but it has a lot of flaws. I like iron man 3 a lot more than most but it also has a feature that never stuck going forward and that is extremis. But I like the story even if Killian never developed as much as he should have.