What a great manga! Don't expect life changing, earth shattering, soul-deep stuff here. Instead, expect to find yourself greatly entertained with endearing characters, honest humor, character-driven plots and little hints of something more between Shin and Yankumi.
If you've seen the drama, the manga is hardly like it. There's a lot more fighting and yakuza-centered plots and, I feel, a more interesting relationship between Shin and Yankumi. (Not to mention, the entire 3-D class doesn't all move around together like a herd...) Yankumi isn't as clumsy or as into making cheesy speeches and crying all the time. Also, I miss Kuma's ridiiiiculous scooter that Shin would hop rides on, haha.
I've only watched up to episode 9 of season 1, but so far Shin and Yankumi don't at all interact the way they do in the manga. In the manga, Shin sleeps on the school roof a lot and Yankumi often bursts in on him asking for advice (yeah, she asks for his ADVICE--haven't seen that in the drama yet!). He isn't as confrontational in the manga (the only time he really got pissed at Yankumi was when she told him to butt out of her yakuza life). He often tries to save her but ironically, he always gets beaten up and she ends up saving him.
Anyway, I'm not at all dissing the drama. I don't think it has to copy the manga to be good and I enjoy it for its unique interpretation of Gokusen. However, I vastly prefer Shin and Yankumi in the manga.