Do not watch this after the anime series! Either watch it first, or wait an amount of time, it was a bit of a let down for me, because it was re-telling a story I already knew and was of, in my opinion, worse quality than the anime. Story: The story is fairly short, only covering a few chapters worth of the manga to tell what is one of my favourite early arcs of the story. The story was quite good still, and it stayed faithful to its source without making crazy changes like some do. 8/10. Art: The animation of this OVA was not to mypreference, I did not like the full body colour changes of Koro-Sensei, and I think that it was a bit awkward looking at times. That being said, it was never bad, so 6/10.

Sound: The sound-quality from what I watched (may have just been my stream issue or something) was fairly poor, but the background music was alright. I don't think that a deep voice really fits Koro-Sensei's character, nor did I particularly like any of the other cast choices. 6/10.

Character: The characters themselves, were left perfectly fine, but as it is an OVA none of them had too much depth, that being said they were still adapted quite well, 8/10.

Enjoyment: This is based on my experience, and I am giving it a 7/10 for enjoyment, that is factoring into account everything that I just accounted for and my personal feelings towards it when I watched it, feeling that it dragged on a bit.

Overall: This was not a bad anime, but I think I ruined my experience of it by watching the main series first, which is definitely the better adaptation. In saying that, I still think that a 7/10 is a fair score, I would recommend this, but only if you were willing to watch the main series afterward, or had some prior manga experience for more context on the characters.