Mr. Brandon James Routh, for all his superficial resemblance to the late Mr. Christopher Reeve, was actually a poor choice for the dual role of Superman and Clark Kent in Superman Returns for a number of reasons.
First, Mr. Routh was unwilling to dye his brown hair black for the role; besides which, he styled his hair too tightly when geared up in Superman's uniform. These reflect that the super-human identity was apparently shown to be more uptight than the human identity when in reality the reverse is supposed to be true. In Lois And Clark, Mr. Dean Cain did just as bad a job, likewise showing Superman to be more uptight than Clark.
Second, Mr. Routh's uniform had coloration that was too dark for the character. Moreover, its belt had, instead of the gold oval buckle of the comics, a badge-like buckle whose coloration was a color reversal of a badge that looked entirely unlike what the badge was supposed to be. Bryan Singer's company is called Bad Hat Harry Productions; its logo is an animated cartoon re-creating the scene from Jaws in which Martin Brody says to a man called Harry, who is wearing a hat that resembles a shark, "That's some bad hat, Harry." It is all too easy, similarly, to complain to Mr. Routh, "That's some bad suit, Brandon."
Third, Mr. Routh had absolutely no acting stature by comparison to Mr. Kevin Spacey, whose laughable in-character excesses of performance made him as poor a choice for Lex Luthor as Mr. Routh was for Superman or Clark. Part of what makes Lex Luthor what he is in the comics is his almost-total lack of a sense of humor. After all, in the comics, Luthor blames Superman for both his total and permanent baldness and the catastrophic loss of one of his early scientific experiments, an attempt to create protoplasm from chemicals.
Fourth, Mr. Routh showed no capability of making his Clark believable alongside Ms. Kate Bosworth's Lois Lane. Throughout the film, he made himself seem to be almost an empty suit, smaller than life-size, and to shrink rapidly--all through no fault of his own.
But in no way should this reflect an endorsement of Mr. Thomas Welling in the role--he squandered all HIS credibility with his involvement in Smallville. Sad to say, there are few contemporary actors who can truly fill Mr. Reeve's cape and boots as Superman AND his drab suits and ugly pairs of eye-glasses as Clark, and Mr. Welling is not one of those few. Nor is Mr. Routh another.