Finding the right balance between irony and seriousness in sci-fi and superhero movies has been a long, complex, dialectical process. And at some point, I think film historians are going to look back at 90s-ish movies and realize that was a bizarre time of non-realistic, mannered films in general -- witness later Schwarzenegger efforts, 2000's Charlie's Angels, or the strange and more obscure action film The Big Hit -- though The Matrix helped convince everyone you could do serious-feeling fantasy stuff without apologies.
In superhero movies, you could see things careening from the fairly realistic-feeling Superman: The Movie to Burton's kabuki-like Batman (which the recent Watchmen movie resembles more closely than the Nolan Batman movies do, really)…and years later the audience-pleasing -- but still ever so slightly awkward -- first Spider-Man movie…then the impressive but by some estimations over-serious X-Men 2 and then -- bingo! -- to the first Iron Man, which seemed to please everyone for the simple reason that it had jokes but not of the kind that undermine the reality and intensity of the story conventions or make the genre seem pointless (which I could have told them from the get-go).
At last we had found our Irony Man, if you will. I look forward to seeing what Joss Whedon does with the related Avengers movie in one year, script-wise more than fx-wise.
Audiences like comedy. They do not like being told that the whole act of seeing the movie is a big, pointless joke on all of us. It is amazing that Hollywood, which is hardly avant-garde, does not really understand this simple rule of realism. George Lucas, for all the love and attention he lavishes on his universe, doesn't get it or else he would not do things like put a wacky Bob Costas-sounding sportscaster in a Star Wars movie, much as I hate to mention that shudder-inducing example.
The past few years have seen a big increase in what we might call the "sci-fironic" mode in pop culture, too, with the hipsters adopting enough nerd tendencies to feel comfortable invoking robots and clones and the like for both comedic and cool purposes, without any longer feeling the need to explain. X-Files probably helped pave the way, as did all the sci-fi-like jokes, often cropping up without any felt need for context, on The Simpsons (e.g., "I need tungsten to live!").