I've always liked that Iron Man didn't go overboard with recurring villains. I mean, I am so sick of stupid Lex Luthor having to be in everything Superman. The Batman movies etc have at least gone beyond Joker, but every time I see Supes, there's that bald git in a sport coat.
Iron Man had a steady gang, but they weren't over used. I loved the Controller, for example, he was creepy. But how often do I need to see him around, pulling out the same bag of tricks?
Also Iron Man either outgrew his foes (Melter... stripy pants just aren't as imposing as they used to be
) or they were part of the political climate of the 60s that is no longer relevant for the hero today. A writer either has to retool them or make new ones.