I agree with whomever said every drama addict should watch Gokusen, at least one season. It's not a question of taste: Gokusen is a roundup of unforgettable characters, first and most adorable of all Yankumi. Yankumi is in institution in the j-drama world, and although season after season the situations she's thrown into repeat themselves, or perhaps because of it, most of her sentences, gestures and mantras have become a milestone. There's nothing particularly original in the sub plots regarding the students: they always get in trouble until she comes to the rescue and teaches them that true friendship conquers all and it's important to fight for the people we love. But despite the trope and the dejà-vu feeling, I enjoyed all 3 seasons and even watched the movie - without liking it much, though. It was too hasty and didn't bring anything new to the whole. I think it was meant to gather up old and new students, and I admit it was great to seem them all again.
Therefore, I'm all for listing Gokusen among the must see dramas. If the plot does not appeal to your taste, think that it's like watching all the japanese idols move their first steps in the business.
Oh, and let's not forget the Yakuza family: hilarious, sweet and, again, unforgettable! :D