I've seen all the versions of GTO including the anime and the live action drama and movie, and I still think this manga version is the best. It includes a lot of material that's not covered in either TV series, bringing Great Teacher Onizuka even greater challenges from the class that has vowed to either get him fired or willingly quit, and the faculty that despises his nontraditional (if not downright insane) teaching methods. The plots against him get more and more insidious, culminating with the introduction of a new school head mistress who is hot but who also redefines the word b***h. But no matter how badly his situation spirals out of control, Onizuka is always able to turn it into some sort of life lesson for his students where he is able to make them see life in a whole different light.
This is probably the crudest version of GTO compared to the others (not that that's a bad thing). The anime was cleaned up a lot, removing the references to Onizuka's extensive porn collection as well as his extensive group former biker-gang buddies who are involved in all kinds of shady dealings from drug trafficking to ... well, I don't want to ruin it for you. The live action TV drama did include references to his video collection, but even then it didn't develop that side of Onizuka to the extent that the manga does.
Actually, Onizuka's perversion is an important aspect of the manga because, even though the other teachers are just as bad as he is, Onizuka is the only one who is honest about it. And it's the fact that he is an open book about everything that wins his students over in the end because they realize that if he's honest about that then he's honest about everything else he tells them.
That's not to say that it doesn't get him into a lot of trouble. In fact a lot of the plots that are hatched against him try to take advantage that he is a 22-year old virgin who is looking for "love". I mean, you know that he's going to win over his students in the end. That much is predictable. It's how he gets to that point that makes it hilarious and unpredictable. That's because it seems like almost everything he does is just to satisfy himself of to save his own butt. Still, no matter what he does he just seems to be making it worse for both himself and his students, but in the end he turns the situation into a lesson for his students.
The art in the manga was more realistic than you will find in your average manga. The characters all have distinct and believable designs. Sure there are some characters that are generously proportioned, but even then the designs are believable. Of course, the classic trademark of GTO is Onizuka's facial expressions -- they are realistic (I have to laugh just thinking of the author looking in the mirror as reference material) but ... well just check this out:
The end of the manga was much better than either the anime or live action drama. Both of those just have Onizuka leaving the school after his job is done. While the manga has probably the most over-the-top ending, it's much more satisfying and dramatic and, I think, fitting for GTO.
When I finished up the last volume it was kind of a bitter-sweet send-off. I know there's the Shonan Junai-Gumi manga (as well as Bad Company and the associated anime and live action versions) but that's not nearly as good as GTO so I'm really going to miss it. Sure this has some crass humor, but it's balanced by a lot of heart and comedy, all making for a fun and unpredictable story. If you haven't checked out GTO yet, go pick it up. All the versions are great, but the manga is still the best.
And just for the heck of it, here's the openings for the TV versions: