I think the reason people find it missing something or drawn out is because they are comparing it (maybe even subconsciously) to X-men and Spiderman whch have really shoddy loosely put together plotlines but incredible action packed sequences that make you not care....
The difference with Iron man (and i saw it last night also) was you throw in Jon Favreau, A name thats becoming bigger and bigger with director under his title and you get exactly this..
Solid Character development
Solid plot
Solid flow
The formula was almost generic but it was safe, I guess if i had to try to bash it, which is hard because I really liked it... I would say...
X-men left me wanting more because there was so much great action
Iron Man left me wanting more because there wasn't as much action as X-men.
Ninja Edit: I missed the end of the credits, someone please spoil it in PM