It's hard to give an unbiased opinion on GTO, simply cause I love it too much!>
Don't listen to what people say about how the characters are static, boring, unsophisticated. One thing you have to keep in mind this was a shonen manga back in the day. Another thing It's not true. It's an honest story about how a feared ex-delinquent, stumbled upon a teaching career (due to a stupid misconception), and actually falling in love with his career, and for the first time in his life he (arguably) gets his shit together for the sake of his students. He's dumb, lacks common sense, and technically by our standards, lacks everything we expect to see in a teacher, but he has comion- something that we now believe teacher's lack. He goes through the depths of hell to help his students and educates them on something more that's important than school work. He teaches them the importance of authenticity.
I love fujisawa tohru's works, my cousins used to have all his series, so I grew up reading them. I have to say GTO is by far my favourite, and it ultimately helped inspire me to become a teacher too (or atleast I'm on track to). It also give you (a dated, but arguably still functional) insight on delinquent culture in Japan, and explores why students abandon education & become what society deems to be "dysfunctional". The series also gives insight to how the institutional structure of the education system are slowly failing, and how we should revitalize it (in this case this job goes to Onizuka).
I honestly love this series, and I believe it's a must read for everybody. I grew up kind of like a delinquent, but honestly my teachers, and this series altogether helped me a lot. I believe everyone should, for the very least, give this series a try (like first 15 chapters and everything just starts moving). I also hope for those new readers to have a great laugh and enjoy his stupid antics, and overall perhaps find it just and inspiring as i do.