Isn't Extremis considered one of the best storylines in the IM comics? I'm surprised they didn't go with that stroryline for IM2, which ended up just being an Avengers trailer.
This gets said far too often and now that I've rewatched IM2 a few times (just got the disk after Avengers) it really seems unjustified.
There is one short visit by Nick Fury mid-film where Tony says "Is this about the A..." and Fury cuts him off and brings it back to the main plot. There is the presence of Black Widow which had nothing to do with the Avengers movie except she was in it too; it's like saying Pepper being in the Avengers made it an Iron Man trailer. Then there was the credits scene. That's it. There was nothing past those few seconds with Fury where they didn't talk about the Avengers, that really tied it to the Avengers; it was all about Tony, his despondency about his failing health, his walls (armour) put up against the people around him who cared, his dealing with living in the shadow of his father, and realizing his dad really did think something of him which turned him around.
The plot was about Tony Stark, and the conflict with Whiplash/Dynamo was a thin layer on top of that. So if you go in thinking that Whiplash is the main story, yeah it seems thin, but if you see it as Tony's story, not Iron Man's, then the movie is actually about something. It really does take the character from one place to somewhere else, a place where he's ready to step up and be an adult, not a child. This has nothing to do with Avengers.