Ultimately, I think Iron Man 2
's problems had more to do with lightweight villains. While Whiplash was a mean lookin' mofo, he pretty quickly had his ass handed too him in both fight scenes.
I think the Avengers elements weren't handled too badly. Yes, they felt more like promos for the next movie than a legitimate part of this one. But overall, I didn't find them too intrusive. I thought Black Widow could have used a bit more development actually. As for Nick Fury's role, I suppose I would have to know more about how those plotpoints would have progressed without him. He did provide a necessary stepping stone from A to C.
The only part I didn't like was when the Avengers provided some sort of temporary stop-gap for Tony Stark's blood poisoning. I felt that really sapped the urgency out of that plotline.