I thought Routh was great as Clark, but I didn't care all that much for his Superman. Some of his delivery just seemed... off. I could see if they were going for something where he was having trouble readjusting to being Superman or dealing with people after his return, but he had no problem slipping back into being Clark Kent at the Planet, and his Superman never improved, so I just have to chalk it up to a less than stellar performance.
Still, I'd be perfectly willing to give him another shot.
I also thought Dean Cain was a much better Clark Kent than he was Superman. He just never seemed all that comfortable in the suit, while his Clark felt much more natural. In fact, Cain's Clark, modeled I believe on the more confident John Byrne version, I thought was actually quite good. If that's the kind of Clark they want to go for in the new one, I say bring it on.