At first sight, may sound lame like those movies from the 80-90's where a moronic teacher arrives at some school and all of the sudden the students are touched by his 'something' (I can't see what they saw). But don't worry, dear fellow, it's not GTO's case.
Few people can see that, but GTO's comedy is just a disguise. There are self-evolution on Onizuka's acts, acts that often remember the teachings of Osho, an indian spiritually incorrect mystic. The strenght of the anime isn't the story itself, but Onizuka.
The anime follows the manga 'til vol 18. Read it.
The live action is some freaking bullshit, not enought to ruin Onizuka completely, but can't avoid the 'love-story' bullshit from all the japanese soup operas.
unfinished review
