I'm a bit baffled by the blue streak in Mu Yan's hair. I'd read theories that it was to justify his "Xiao Lan" nickname (since he doesn't appear to be wearing any of Mu Yan's signature blue robes...), but that makes little sense when the main character herself appears to have a blue streak as well. I mean why refer to another character by a characteristic shared by yourself?
Though Kevin's face is a far stretch from how I'd pictured Mu Yan, I do think that he has the acting capability to potentially pull it off judging by his performance in Bu Bu Jing Xin.
I'm definitely looking forward to seeing Yuan Hong's Shen An as that was one of the most memorable characters for me personally. (novel spoilers):
click to show/hide spoilers
It's been years since I've read the novels so I'm going off pure memory here.
Based upon the fact that he pledged his life to Liu Qi Qi purely since she was the one that he believed he owed his life to, in a sense he's actually a very loyal type almost to the point of stubborn stupidity. His initial hatred towards Song Ning is understandable since while she idolizes him, to him she's part of the enemy that killed thousands of his men/subordinates/companions and has just politically forced him into taking her as his formal wife. Being forced into submission both on the battlefield and even in his private life must have been a significant blow to someone whose never lost previously.
After reading a spin-off Shen An-centric chapter from the online txt version of the books (and which doesn't appear to be in the paper copies I purchased later on), I felt that while his actions were not completely justifiable, I could sympathize with him as a character. I think that given how Yuan Hong usually succeeds in creating the most charismatic villains, his Shen An is definitely something to look forward to!