There is also a TV movie and an OAV
special. Nice tidbit of information: Takashi Sorimachi
, the actor of Onizuka, and the actress of his love interest Fuyutsuki-sensei became a couple and eventually married in real life.
Basically, the main point of the stories is that Onizuka is outwardly rude, lecherous and agressive - exactly the kind of guy no father would want their daughter to date - yet it turns out that in truly critical situations, he shows far more integrity, ethics and selflessness than any of the higher-than-though people who look down on him and bad-mouth him. For example, while he loves looking under girls' skirts, he fends off several attempts of schoolgirls to seduce him; in contrast it turns out one of his worst enemies among the teachers is habitually groping women on crowded trains and another put cameras in the girls' toilet. In a way, it's a statement against judging people by appearances.
It's also quite interesting to look at the differences between the manga and the dorama: because the TV drama has only 12 episodes, the writer had to select which of the manga stories to use, and in order to keep it coherent, many details had to be changed and some roles were merged. However, they did a good job, and both versions of the story are equally funny, exciting and sometimes touching.