In my opinion, Lawrence Ng did a great job of portraying Zhang Wuji opposite Gigi Lai. I was annoyed at first that he was old looking but I saw his charmed as the series progressed. He did a great job, if he was in his twenties, he would have been in the same caliber as Tony Leung.
As for the whole Andy Lau vs Louis Koo debate, I highly think no one is better than the other; they are in the same level of acting greatness. The two are equally adept and incomparable. Nowadays, Andy Lau is still great in acting, can't say the same for L.K though. Have you watched Andy Lau in The Flying Daggers or The Deul? Andy Lau stil has it. As for L.K. have you watched The Chinese Ghost Story 2011? His acting wasn't so memorable. But both deserves praise for their portrayals of Yang Keur. Andy Lau is Andy Lau and Louis Koo is Louis Koo, they're both very big stars and very talented, Andy Lau just a little bit more talented throughout his filmography

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Hu Ge is a freaking fag, (no offense to any here) he shouldn't be acting in tough guy, wuxia roles. He's great an actor but he aint no tough martial arts guy and he can't sell it. I'm always gonna see him as a joke. The kid can act tough, I'll give him that.
I think Huang Xiao Ming did a phenomenal job of portraying Yeung Kor. Its a very hard role because its been done over and over again, and its a "make it or break it" career move. Its a lot of pressure, I'd imagine. So he has to bring so much to the table and he had to appeal to a new audience and gain respect and love from the old audience. He had tough shoes to fill, apparently his feet were big enough, kudos to Xiao Ming. He also did great job in Ip Man 2 as Ip Man's first disciple.
If you watch Chu Liuxiang 2007, you can better understand my point. Ken Chu has failed as an actor, he couldn't gain the respect and win the hearts from the people that grew up on the old Chu Lau Heung, played by Micheal Miu.
Ken Chu simply could not fill Micheal Miu's shoes. But he did a decent job, he is not a bad actor, this just wasn't a role meant for him to play. He wasn't tall enough, handsome enough, and experience enough to play Chu Liuxiang. Some scenes were just pathetic to watch for me. But I enjoyed the series overall. Maybe Raymond Lam should try to play Chu Liuxiang?