Episode 5 is the only one which is very confusing that I saw so far. Mainly because they made the story shorter. There are many past stories but they chose to put those in one episode. They combined two or more stories into one. I'm not saying that it's not good. But it's not something you can enjoy if you don't know the whole story.
When I watched the season 1, I didn't know the whole story. But I could follow the story. After I watched the season 1, I started to read the novel. Season 1 is very easy to understand. Even if you don't know the whole story, you can enjoy the whole season. But this episode is not. I feel like they have changed a lot and also combined a lot into one, I kind of nearly lost in the middle. If I haven't already read the novel, I'm sure I'd be lost. So, I'd say if you watch this episode, you have to make sure that you've already read the novel. Otherwise, you won't get the whole story that much.
As I've mentioned in above, they have changed the plot as well. It gives the fans a new taste if they like this kind of changing. If they don't like, there will be a lot of arguments. No matter what, I think it's still okay as long as it makes sense.
All in all, although they have changed a lot of things and combined many things into one, the story still makes sense. The last scene seems to be different, but we all know how it would turn out. In this season 2 xian yun pian, they always bypass and when it gets to the end, the result turned out to be the same with the novel. Anyway, I just love Mo Dao Zu Shi no matter how much they have changed. So, I can't wait to see the next episodes.