Yes, Wen Ning's personality changed a little from The Untamed, but to be honest, it wasn't so dramatic that I didn't know who Wen Ning was anymore. It's almost like Wen Ning has just matured, which is expected. I still recognized his character.
As for the story, wow! Blown away! Just like the drama, this spin-off movie had a really good supernatural story to go with it. There was even a huge twist that I didn't see coming! My attention was kept throughout the whole movie. I really liked it. And the acting was amazing!
You should watch The Untamed or read Grandmaster of Demonic Cultivation before watching this, so that you know Wen Ning and Lan Shizui's background. Their characters are not further developed in this movie. You just have to know who they are.