Weakest part so far. And I stand by it. I think it has to do with the fact that I don't see Ryo as capable of killing. He doesn't strike me as the type to take someone's life. He couldn't even kill Chunyan in a moment of life or death so I really fail to see how he will bring himself to kill Lan Di if given the chance. He just doesn't strike me as having it in him to kill someone. The thing that has always driven me moreso is the mystery behind those mirrors and what actually happened between Iwao and Lan Di's father. And the martial arts aspect. Ever since the 2nd game, I feel like I took more interest in the greater picture over the revenge story (which is where my personal disappointment of SIII lies as I thought it would be the moment of Ryo realizing the bigger picture around him...but hey we still have more chapters to go so I guess I will have to wait and see. Maybe getting his ass handed to him by Lan Di will change him in SIV?)It's not been completed so how do you know if it's good or not? It's the main driver for the series.
But if I have to be honest, the revenge part of the story so far really has just been initial motivation to take the trip. You're right, I don't have full context of the story to fully judge it but as far? I'm not really here for the revenge story anymore personally. I'll be keen to see how it plays out but my main interest lies around the larger picture. I'm here for the mystery around what those mirrors actually do and the mystery of what happened between Iwao and Sunming Zhao. That's personally what drives me with these games story wise moreso than the revenge plot.
If I were a betting man, I don't think you'll ever see Ryo get revenge (which will probably piss more people off if so). I think a fork in the road will come that will change the story. But we will wait and see.