SR was OK. Not great, but not terrible. Casting Routh as CK/Supes was a good move because of his physical resemblance to Reeve, but his acting chops are ... limited.
Regardless my opinion on Superman Returns, I've never been one to criticize Routh, simply because he didn't really have anything to do. Aside from a few strut and pose in the costume he hardly has any memorable material in the movie, which is rather pathetic given he is the titular main character. Hell, I think Ebert even mentioned in his review that despite being the lead, Superman probably had the least amount of dialogue.
Routh may be a good actor, or he could be a horrible one. But I'm not going to base my opinion of him on Superman Returns.