I'll start off to say I really did enjoy this movie! Yes, the plot is VERY different to the first - but this isn't about the White Snake anymore, now we get to see her 'sister' and her story - which yes, is a VERY different experience.
I'll say that while I loved watching the first part where the two go to destroy the pagoda - plot-wise it was very confusing unless you already have a good outside knowledge of the legends. But it is really a beautiful sequence.
The quality of the animation is stunning!! A huge step from the last movie.
The only issue I have with the plot is that for me, it felt like nobody changed. Verta grew into more of an actual personality in comparison from how she was in the last movie - but nothing was learnt! Not all movies need morals or a learned lesson, but I feel like none of the characters learnt or grew in ways that mattered. Verta at the end of the movie still feels the same as she was at the start - her motives and 'obsessions' never changed. It just felt that in the end, the plot never really went anywhere in that regard. There are a few other small plot holes or things never really explored that would have been cool to otherwise have explained, but to me they are very minor.
Now I'll get into SPOILERS so please stop reading if you really want to go into this movie blind - I do HIGHLY RECOMMEND to give it a watch despite my subjective ideas about the plot. However, if you don't care about that or if you've already seen it then proceed.
One issue I have with an essential part of the movie is with the mystery guy - I was really hoping once it was revealed he looked like Blanca, that it was her SON. At the beginning of the movie we saw her child after all!! Not sure how he would have survived so long to modern times, but it's not the most far fetched thing in this movie. It turns out he IS Blanca - and that Verta was right all along. And it felt that we were back to square one - that Blanca is the only thing in Verta's life and that Verta REFUSES to let anyone else in.
I just feel like it would have been really cool to see an interaction between Verta and the half-breed child her 'sister' had. That would have opened up sooo many cool possibilities! Like she thought it's Blanca, but then they find out that he's Blanca's SON!! Throw them both for a loop! He would never know his mother, and the last person he saw before he was taken was Verta - he was only a baby so that could be why the face in the water was clouded!
Verta could grow to accept him as a part of family and love him AS family - see her grow to love more than just Blanca, BECAUSE of Blanca. To see her truly accept more people into her heart... If that makes any sense.
That's the only real gripe I have, and I'm aware it's very subjective. The movie is otherwise really cool and a fun exploration of their world in a mad max end-of-the-world-with-biker-gangs style mixed with mytho creatures. I would highly recommend to give it a watch at the very least for fun.
Hope this helps! :D