He was supposed to come back for a third Batman film, but once Burton's film was ditched by the studio in favor of Joel Schumacher's Batman Forever things took a turn for the worse. The studio offered Keaton $15 million dollars to reprise his role as the Dark Knight in the film, but he turned it down. CBS Sunday Morning asked why he turned it down and he gave one simple answer,
"Sucked. Yeah, it just was awful!"Read the whole article at the link above.