The scripts for the Iron Man films are slapdash messes, and depend largely on Downey's remarkable talent and charisma for any shred of humanity - subtract him and there's not much to draw people in. There's a lot more going on in terms of recognizable human relationships and interaction in Green Lantern than in most superhero films. Thor is completely vapid in that regard, though Captain America looks promising.
Though I suppose a large percentage of the audience for these things is more interested in debating how far someone can throw a magic hammer than in why anyone would care.
Though the Iron Man movies did rely heavily on RDJ, I think the first movie's plot worked. The second one was all over the place. Whereas with GL I don't agree about more going on regarding human relationships and interactions than other superhero films; so much of stuff was done in a haphazard or stunted manner. There never seemed to be satisfying follow through with GL. Why does Hal's brother not like him? What happened to the family after the birthday party, they completely disappeared. And are Carol and Hal back on or what? Though I don't think every t needed to be crossed, but I wish they had at least dealt with the family situation better. It was one of the better parts of Johns' take on Hal for me. It helped humanize the character in the comics, seeing his strained family relations.
With Iron Man in comparison we got Tony and Pepper's unrequited friendship in the first that turned into a capricious kind of relationship in the second (which I didn't like, but it fit with RDJ's take on Tony). With Thor, we got the well rendered sibling relationship with Thor and Loki, the father v. son with Odin and Thor. Granted more could've been done with Thor and Jane, but I didn't think their relationship was completely unbelievable; I think the actors sold it as best they could with what they had.
When I think about it, almost every comic book movie over the last decade has done just as good or better with human relationships than GL. Some that I don't think did, Superman Returns, Punisher War Zone, Blade Trinity, for starters. My memory is starting to fail me.