It's strange. Maybe it's just me, but I've noticed a lot of people who don't like Routh complain about his appearance as being the central factor, and usually nothing else.
I can see why some people think he looks a little young (I didn't have a problem), but I thought he nailed the role. His voice was deep and commanding as Superman, but he was also very sweet and sincere, whether it was as Clark or Superman. Especially his facial expressions--my heaven's, he looked intense as Superman.
I just wish he had more lines.