This is a two-part review, reviewing both the work as a whole and reviewing it as an adaptation of the novel: This season picks up after the original season 1 of BTTH (with an interlude between episode 2 and 3 for the special). The character designs have changed so be aware of that if you came from season 1. Since this is produced around the same time as the first special, it has some of the same problems, mainly some stiff animations during fights. Overall the story is good without any super obvious or gaping plot holes, pretty standard for these xianxia type stories. As an adaptation,this is pretty faithful to the original text, some of the minor details were changed but there was only 1 major thing that got changed (from what I can tell), and that is the departure of Xiao Yi Xian. In the original, she chose to part ways rather than secretly leaving. They also could have done better in showcasing their short time in the valley, they even cut out what I believe was the most important line/quote of their relationship "that regardless of how hated or poisonous she became, he would eat her food regardless (despite the danger of being poisoned", it's actually this quote that led to their unbreakable friendship later.
Adaptation score (how faithful to source): 9/10.