Rockstar almost suffered detention for this one.
There is only a slight leash this game has on you. You are supposed to attend class. Yeah, yeah, i know. But class takes up only a tiny fraction of the game, and the rewards for passing each class are quite enticing. For example, paint a picture in art class, and you'll learn how to sweettalk the ladies. Find words in an anagram for english class, and you'll be able to taunt students or appologize to authorites. (Take that, Speechcraft!)
Chemistry and Gym will probably wind up being your two favorite. In the lab, you'll figure out how to conduct weapons. Firecrackers, itching powder, and marbles to name a few. These can be used on anyone. Although it's highly discouraged. Gym class teaches you how to throw a punch and virtually humiliate your classmates with a fury of fists.
In Grand Theft Auto, the background story is simple. You owe someone some money. You're supposed to get it back to them. But things change for the better and worse as you progress. In Bully, all you really have to do is pass class for the year. But in doing missions, ugly variables rear their heads in protagonist's Jimmy's way.
There is SO much that can be done in this game. For a reference, check your STATS section of the pause screen and refer to list of things done. Quite frequently I checked the page in amazement saying "I can really do that?!?". Even if you never play this game more than once, it more than makes a name for itself in just a few minutes of gameplay, keeping the story interesting the entire time.
It's only downfall may be the content. Rockstar had a tough time releasing this game, seeing as succeeding promotes violence in a school setting. I think we're passed the age where the problems of today's youth are focused on videogame content. But the FCC raises a point. You really do wind up punching the daylights out of almost everyone. In town, you can pick on the civilians or even punch an officer in the balls. There is no bloodshed, and nobody dies, but all the same.
STILL, the almost unnacceptable wrongdoings you are capable of nowhere near overshadow this game's ability. This game is just way too fun. Disclaimer: you will probably not see your pillow for a while. Just sayin.