Warning: Some spoilers
As a viewer of the show, I noticed both positives and negatives in this movie.
On the positive side, the animation was stunning, Marinette's character was less creepy, Adrien standing up to his father was refreshing, and there was some remorse shown by Gabriel (I still like the show’s version of him, though, adds more drama.) The chosen voice actors for the songs were also good.
However, there were some downsides. Marinette's English VA for the songs didn't match the one playing her, which was quite distracting. The love story between Marinette and Adrien felt rushed, as did the ending. The movie's transitions and flow weren't smooth, and it seemed like they cut out scenes to accommodate the songs, which were a bit repetitive.
Overall, I believe this movie had great potential, but it fell short. The story and singing were alright, but the excessive focus on the songs seemed to impact the storytelling negatively. Personally, I rate it 3 out of 5 stars.