Routh has always seemed likable to me, but I don't buy him as Superman (or even as Clark Kent). There's no hint of a commanding presence. Something is off about him physically, as well - something other than his unduly slim physique.
I might like to see (a somewhat more muscular) Tom Welling in the role. His performance in Smallville's 'Noir' indicated an unexpected ability to play the coolest, most confident, one-step-ahead-of-everyone-else guy in the room - and still seem like good guy doing it. With a haircut, a deeper tone and a more confident bearing, he could be an excellent Superman.