There are 3 movies to watch basically. I will not détail the plot but just mention I really like this type of thriller movie set in Japanese school context and I thought the idea was really interesting. I would say the first part got me interested, thought I felt some really big budget concern on this movie. The second part was a pain to watch, the movie tries to deepen the characters but it just feels like never ending discussions. The 3rd part was ok, then it is up to whenever you accept the ending or not.
Overall there is a really good premise for this movie but it should have been reduced to 2 movies. Interesting ideas but could have been much better than the final result this trilogy turn to be.