I play the game in Japanese, so I had to go back and listen to the cutscenes to see first hand what people are talking about. And yes, it's terrible. Everyone already noticed it before the expansion, and despite the hopes of some that the quality would improve in 7.0, apparently the same issues are still there. The acting range is not very good, and both the tone/pitch and accent sound really forced, especially at times (and worse, it's the most important ones, like when the actress should put her all in delivering an emotional line).
I think that an effort is made, but the talent and/or experience to achieve the intended result is not there. As I commented when this was discussed before the expansion, the actress tries to do many things at once with her voice because they don't come naturally to her, and ends up failing on them all. Moreover, due to focusing on that the acting also suffers.
It was not the best casting for a character with so many lines of dialogue, where these issues become even more glaring. For that reason I can definitely see it downgrading the whole experience, and I can understand people's complaints.
