In the book the BR game is more well-known, and feared by the students. They are clued in to what is going on much earlier.

The novel is also much more overtly set in an alternate-history world where Imperial Japan survived WW2 in some undisclosed fashion (it didn't win, since the USA is referenced and the main character is a huge Bruce Springsteen fan) and the county is a dictatorship with no human rights. The movie is much more vague on what is going on in the outside world.



Evil Teacher in the movie isn't necessarily entirely Evil, just being worn down into doing something terrible by the system and his horrendous relationship with his wife and daughter. That scene (a flashback to an incident back at school when he counselled Noriko) was a brief display that there is, or was, a real human being lurking in there somewhere.



Good Transfer Student got into the game again surreptitiously to sabotage it from the inside. Demented Bad Transfer Student got in officially to make things more interesting for the players.

In the book, IIRC, Bad Transfer Student is actually a normal member of the class who just goes nuts when put on the island.



Correct.



Before he dies, the teacher has to round off his troubled relationship with his daughter (which has been ongoing through phone calls and messages throughout the movie). If this was a mainstream Western flick, he'd make his peace with her. As this is a f-ed up Japanese movie, his last act is to tell her to ESAD instead.



It's a call-back to a relatively normal time when the kids in the class interacted with one another normally. It's meant to show how far they've fallen once they're on the island and out to kill one another. Or something.



Stupid Girl and Whiny Guy are wanted less for murder than for basically escaping from the game and breaking its rules. Also, and the film is vague on this part, after they get back to the mainland they become terrorists, join up with other dissidents and start blowing up government buildings in a fit of freedom-seeking vengeance.

The movie's sequel (the book doesn't have one, yet) goes into that a little more, but is hamstrung by the director going stark raving insane due to 9/11 and using the film to bash American foreign policy repeatedly in a manner that totally destroys any coherent point the film was trying to make. It's worth watching for the bit where they take the mickey out of SAVING PRIVATE RYAN's D-Day landings though.

I'd strongly recommend reading the novel, which is better than the film. Also check out the Wikipedia entry for the movie, which clarifies the plot a bit more.