Speaking to the Los Angeles Times, the Tropic Thunder star praised the first film in the comic book adaptation series but had few good things to say about the star-studded sequel.
“The first one changed everything for me,” he said. “And with the second Iron Man there were certain aspects that were dissatisfying and disappointing to me but at least they lit me right.
“(The first one) was a meditation on responsibility and an exploration of how a small group of people can take a two-dimensional idea and, if the winds are right, create something that makes people say, ‘That was my favourite movie of the year’.”
Downey Jr cemented his comeback from several years of drug abuse with his role as Tony Stark, and 2008’s Iron Man was praised by critics.
But the 2010 sequel – also starring Scarlett Johansson and Mickey Rourke – didn’t fare as well, with just a 57 per cent approval rating on Metacritic.
Downey Jr also told the Times that he thought his controversial “black face” role in Tropic Thunder – for which he was nominated for an Oscar – would undo all of Iron Man’s solid press.
“I signed up to do it and then I did Iron Man and I thought, ‘You know, I think I just buried myself. I did a movie that is going to re-establish me here in a little way and now I’m going to squander any good will I have.’
“This movie ended up being the most cathartic thing I had done in ages and one of the happiest times in my life.”
Downey Jr is contracted to star in Iron Man 3, reportedly due to begin shooting later this year and due out in 2013.