The main thing is, everybody loved Christopher Reeve.
Gene Siskel called him “totally believable,” and Jack Kroll called him “ridiculously good-looking” and “a delight”. Vincent Canby said “he manages to be both funny and comic-strip heroic without making a fool of himself,” and Roger Ebert said “Reeve sells the role; wrong casting here would have sunk everything.”
Even Pauline Kael said that Reeve was “immediately likable”, and she hated the film worse than she hated kidney stones and road accidents.
Superheroes Every Day 