A (rather) small review of all 3 seasons (because they are really cohesive parts of one story). My overall score is something like 9.5/10.
Pluses:
+ Outstanding and diverse characters. Ironically, I consider Mashiro Moritaka (the main main hero) as the worst one (7/10) for being quite predictable, stubborn, and boring. Almost all other characters are great: they have their strengths and weaknesses, play rather big roles in different plot points and rarely feel obsolete or forgettable. Some are very charismatic.
Best characters imo: Niizuma Eiji (who might have expected?), Hiramaru Kazuya, Yoshida Kouji
+ Interesting and generally pretty great plot for such a setting. Personally, I haven't expected it to be this good. In other words: It's not very active anime, but still feels quite intense on events and almost never feels boring
+ Inspiring and motivating while being rather down-to-earth and realistic. Good morale, doesn't feel fake
+ Occasionally great comedy
Neutral:
± Not 100% realistic. Sometimes, if thinking critically, heroes may be observed as rather lucky (not only MHs) or maybe too smart. This invests in an interesting plot so I don't really care, also feels pretty excusable.
± Many shounen-style rival clashes in an anime that doesn't really have fights. This was a popular dynamo in many plot moments. Curious
± Art is mostly simple, but it doesn't feel bad. Also, occasionally there are pretty good shots which mostly involve into comedic aspect. Heh
Minuses:
- A few dramas felt dragging and weird to me, mostly including Mashiro and Azuki.
- In the first season Mashiro was an especially big donkey at times.
(those are the main reasons why I don't want to put Story as 10, and also lower my scores for 1st and 3rd season to 9)
Comparing to other anime I've seen: this one has one of the biggest amount of developed and interesting characters. Also, a rare one having nice 'Chaotic-good' characters.
In general: Charming, inspiring, interesting down-to-earth anime, with heavy investments in its characters, which makes it unique and pretty darn great.