I've never seen the Hobbit movies. I am using that as a reference point due to what I've heard regarding the filming process, where Peter Jackson dove right in with no prep work and just went with it the best he could. To me, Iron Man felt like someone coming up with ideas and never bothering to flesh it out. The two things that make it feel that way to me are the dialogue and the action scenes (well, the last battle, as I don't much remember the other action scenes). And really, the only reason I remember the last battle is for how underwhelming it was (although in fairness, I was expecting something epic due the hype). Like Favreau just gave the storyboard artist bare-bones instructions so they'd have something on paper and they just ended up going with it. I mean, from a technical aspect its fine, but it didn't strike me as very interesting. Certainly nothing to warrant the lavish praise the movie got. And the dialogue, again so bare-bones that the fact that it was mostly ad-libbed is completely unsurprising.
I mean, RDJ does a great job as Stark. I guess I'm not a big enough fan of Iron Man where that sells the rest of the movie for me.