The Badger wrote:
He stated that he quit because he was unhappy that the role of Batman was being increasingly over shadowed by the bad guys and sidekicks. http://www.ew.com/ew/article/0,,291605,00.html
It's also been claimed that whilst on the set of Heat one of his co-stars (either Al Pacino or Robert de Niro, I can't remember which) ribbed him mercilessly for appearing in a comic book, kids movie.
That was a rough time for comic book movies. High brow actors frowned on it.
Only those actors that didn't mind doing a "silly comic book" movie would sign up.
Now it's different with comic book movies getting Oscar nominations
I think that argument is somewhat difficult to accept. In Superman the Movie, you had Marlon Brando (double Oscar winner, widely regarded as one of the greatest actors of all time), Gene Hackman (already an Oscar winner for The French Connection, would later win another for Unforgiven) and Terence Stamp.
In Batman, you had Jack Nicholson (already two Oscars to his name, more to follow) and Jack Palance, screen legend. Christopher Walken (winner for The Deerhunter) and Michelle Pfeiffer (multiple Oscar nominee). There was lots of talk about Oscar nominations for Nicholson and Pfeiffer in those years, though ultimately neither was nominated. Batman Forever cast Tommy Lee Jones just after he won for The Fugitive.
Dick Tracy had Warren Beatty, James Caan, Pacino (who got an Oscar nomination for his role), Mandy Patinkin and Dustin Hoffman.
Even a movie like The Shadow could cast Ian McKellen (long before X-Men or Lord of the Rings) and Tim Curry and the great Patrick McGoohan made a rare but welcome big screen appearance in The Phantom.