5 stars!
It took me a while before I jump into AnsaKyou trend years ago, and boy, I don't regret it. Each student has their own characteristic, charm and talent. I'm quite surprised that I remember almost all of the student at the end of the series.
The concept is...simple, fantastical yet realistic in other side. Which a classroom is where you learn to 'kill', and by which means? I learn along with Koro-sensei the meaning of knowledge and what's the meaning of bloodthirst in middle school.
It also one of the anime that success made me bawled my eyes out