The 46-year-old actor said that the first instalment of the superhero movie - in which he plays the titular role - turned his life around, but thought that the second didn't quite measure up.
He told the Los Angeles Times, 'The first one changed everything for me. 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...'
'I love a good action movie - a Steve McQueen or Tom Cruise or Clint Eastwood, Bruce Willis or Mel Gibson in the right spot, and you smile and say, 'That's what this kind of movie is all about'.'