I think Marvel's trick is to do it earnest, but DO IT BIG. And do it with lots of really interesting eye candy.
People don't really want character studies in genre action films. They don't want campy, self-aware cleverness either. They want actors chewing the scenery and they want everything bigger and better and different and sometimes jaw-dropping and outrageous.
Even LoTR for all its earnestness was at its heart a BIG film. I think that's what made it successful, not all the hairy footed gay hobbits.
You want one or two leads who are at their best when overacting: Nicholson, Willis, Downey, Mortensen.
That would be my advice. Do it earnest, and do it big.