Keep in mind Superman Returns more-or-less did "okay" at the box-office on its own merit and got mostly positive reviews from professional critics. But in another light it "failed financially" because it wasn't saddled with its own budget but a couple decades worth of abortions in attempt to make another Superman movie. The Tim Burton, black-cape Superman starting Nicolas Cage? Hired and contracted people who had to be payed even thought they weren't used, SR had to pay for that and it didn't.
I think on a critical angle the movie was okay but probably wasn't enough
of the Donner movie style that was sort of a campy silver-age way of doing things. The movie was too heavy and wasn't enough fun and too morose. There's a lot of pretty gloomy sequences of Superman looking sad or just blah and not the fun, light-hearted Man of Steel he is. Hell even when he IS saving the day and doing awesome things he looks like he'd rather be at home listening to The Cure.