Where would I begin??! Comics Tony is not nearly as flamboyant, dare I say as "flighty", as RDJ's over-the-top Tony, at least not the 616 Tony. Ultimate Tony is closer in some ways, but there's still significant difference between them. Sure he lives fast and hard and goes for the finest life has to offer, but sometimes I'd even call comics Tony "grounded" and "down to earth" by comparison. He can be much more take charge and aggressive, he can be a real leader! someone the other heroes really want to follow. One of the biggest differences I saw, is that comics Tony knows how to brood like Batman when he gets into a darker mood. Movie Tony, even when he's down he's not "down" like that.
Of course I get there are serious constraints on what you can do in just the span of a couple movies, and comics Tony has decades of experience on his movie counterpart, but if he had enough time I believe he might mature into that guy.