Wish it had more of a closure, especially on the part of relationships, maybe a timeskip could have worked too.
Anyway mostly an entertaining manga for the major half, thing is you can always argue about how cliched or predictable most of the plotlines are but perhaps it's because of Onzika's unique way of solving problems and interactions with some fun side characters, it maintains an enjoyable level. However I felt that the Teshigawara arc dragged too much towards the end(as how the backstory was introduced a bit later than for the dramatic effect), and the last arc was weaker than the rest of the story(although Miyabi's issues were handled in a much better way than the anime). The morale, the life lessons, or the topics dealing with social issues, and how Onizuka is used as a mouthpiece for that, really made it a memorable ride overall.