First part of this movie was a slow burn. I think that most of the people prefer the second part, when hell break loose. On the contrary, i believe that the second part is worse, maybe even significantly worse. It became so extremely violent that it looked almost like a comedy, so to speak. Nothing felt real, it was like a video game, people were getting killed and i didn't even blink an eye because it was not convincing.
The first part felt real though. It was "indeed" a lesson of the evil. It was shocking and thrilling and dark, much more disturbing than the gorefest which followed. Even acting was better.
Overall, i liked it, even the second part was at least exciting and it was a fun ride, as long as you like psychological drama horror movies which turn into a bloodshed. But i could have been much better if it took itself more seriously.