The most important thing about this anime, for me, is that it's unique. It's take on the whole superpower/"magical virus" trope is very different from very other anime I've watched. In fact, it basically approaches the trope from the complete OPPOSITE direction as most animes do. I loved the story behind the school and its establishment. I loved the way the series compares its situation to those of every other country with magic users, because I feel like what was going on outside of Japan was basically what happens in every single other magic user anime I've seen. This was the most attractive part of this series for me. The way it approaches the idea of magic and how magic should be perceived just keeps you hooked the entire time, because it's so fresh and unveiled in a way that just blindsides you with every plot twist.
THAT said, I do think that the one area this series falls short on is plot development. I really enjoyed the overall storyline; however, it seems to me that they just didn't have enough time to develop everything. The first half of the 13 episode series is almost filler and doesn't contribute greatly to the overall plot. In the last half, there were quite a few characters and events that seemed underdeveloped. I think, in the moment, it helps make the plot twists even more surprising and exciting, but once you reach the end it does feel like so many things could have been more satisfyingly developed.
The ending is also an issue with a lot of viewers, or so I've seen. I, however, really enjoyed the ending. I think that, with the way the rest of the series had gone, that ending was really the best one they could have come up with. Again, this series is not your typical magical, main-character-leveling-up-infinitely shounen anime. While there are some elements of that, overall it seemed to be more about the ties between the characters and their experiences together. The ending summed that up perfectly, and I love that the series finished on a hopeful, lighter, but still realistic note. (Realistic as in it's not all happy endings. Some things that were broken are not yet fixed, but the audience is left with hope that they will be in the future.)
Overall, this series was great to me because it presents a different image of how things could go if magic suddenly appeared. While not the most masterfully developed, the story is very enjoyable and refreshing. It has a light touch throughout and never takes itself too seriously (e.g. MC never really gives some dramatic/tragic/heroic monologue, thank god), and I think that brighter perspective fits this series very well.
