I think he was fine as Johnny Cage. I'm not familiar with the comic take on the character, so I can't say if he was faithful to it. But GR is kinduva silly concept, IMHO, and a quirky, charismatic actor like Cage was required to pull a movie take on it off.
But as Superman? The Man of Steel should be square-jawed, clean-cut, chiselled and straight down the line. Cage, with his long nose, receding hairline (apparently he and Burton fell out because the latter wanted Nic to wear a rug, Cage refused), distinctive voice, puppy eyes and hangdog face. I mean, how could anyone not tell him and Clark apart, for one thing?
Burton (just) got away with the offbeat casting of Michael Keaton as Batman because the suit and mask helped make him convincing (to be fair, Keaton gave a strong performance despite being totally miscast). But Superman has no mask, can't get away with the raspy voice Keaton gave Batman and has to absolutely look like Superman. Which is not like Nicholas Cage.