I personally didn't even notice the difference until I saw people commenting on it. I don't think there's that much of a difference. The author has just simplified their style a bit to update faster/regularly. I think they did a pretty good job keeping the key parts of their original style while making it easier to draw and color. At the very least it's not like Noblesse where the style completely changed.
Ikr I didn't notice either but I decided to check and it wasn't b ad at all! I feel like people just want to hop onto the hate train that has started. The author made a decision to simplify the art a bit to update more so that people wouldn't lose interest due to slow updates; but also to made sure it still looked as close as possible to the original. The hate is unjustified.
I don't see much of a difference in art I see is that there is less background color,shading,and detail in colors/backgrounds. But it's not as much of a big deal as people are making it out to be. Like chill out it's not as bad as your making it to be. It could be worse ┐(￣ヘ￣)┌