Personality, Charmless and Spying....Christopher Reeve, Richard Donner version of Supperman was charming you kinda rooted for him every time he used those powers. Superman Returns done weird things every now and then like Superman started X-ray visioning people.....spying doesn't sit well with people, for an audience it feels icky and corrupt very ObamaSnowden or the Enron Bush wiretapping scandals.....
Budget, the project was in development for years and kept having to get financial bailout from WB studios. It was supposed to be relaunching the franchise but instead its budget spiraled out of control, despite making millions at the theaters it is considered a failure because its production budget went so astronomically crazy
Going against an Icon, Superman is an icon, he's like Elvis, MalcolmX, Buddha, Santa Claus, Jesus....everyone has heard of his name, knows where Superman lived, they watched the toon or read a comic or watched the movie, everyone has an idea who he is, they know his mum, know his girlfriend, know his job.
Superman Returns in some ways broke the icon, they broke away from the DC animated universe Superman or Reeve / Donner Superman and they gave us a strange, dark, gritty guy who knocked up Lois, flew away to space and generally behaved like a dead-beat dad.
Overall Superman Returns has some very good moments, it wasn't a bad film
but it wasn't a great film either
Critics seemed to like it though because it pushed the right buttons with film buffs and paid tribute to moments in Reeve and Brando history.