Warning: Spoiler warning if you have not seen the first film or read the book.
I had heard the sequel was not nearly as good as the first film (and as I didn't think the first film could have been as good as it should have been, either, I found this slightly difficult to believe). Unfortunately, they were right. The movie picks up three years after the first film. Shuya has turned into an international terrorist, forming a group known as the Wild Sevens (Wild Seven being his own nickname in the book). The government decides to reinstitute the Battle Royale program, though by altering it a bit first. Instead of the class having to kill each other, they are taken to a remote island where the Wild Sevens are hiding out and are told to work together to kill Shuya. Also, the collars are back, but slightly different. They work in pairs now, so if your other half dies, so do you. And to add in some more drama, the daughter of the first movie's teacher transferred herself into the game so that she can take vengeance on Shuya (even though, you know, she hated her father).
This movie did have some really good ideas. However, they were all executed poorly. Whether it had to do with a rushed scripting or the death of the movie's original director early on (his son took over), something happened here. Much like the first movie, I felt a lot was being left out. The movie, to me, might have worked a lot better as a book with a lot more details and background information put in. For instance, I did love the idea of the daughter of the first teacher coming back. Unfortunately, the teacher sub-plot in the first film was not in the book, which is sad, as it was one of the best things about the first movie... so there would have to have been some massive re-writing for the original author to include that whole sub-plot. There was also a cool little connection to Shinji's (from the first movie) uncle, who nobody who hadn't read the original book would probably pick up on. A relationship between those two could have been fleshed out so much better. I also really liked the paired-collars idea, and that was one of the worst-executed ideas. It had so much potential; imagine one of the really good students and one of the more evil students paired together and being forced to work together; one student had a diabetes issue, so she was having insulin issues... imagine the suspense that could have been added for her partner had they done it right. There are so many things they could have done with that idea, and the only thing they used it for was to get the class size down from 42 to 12 in about 10 minutes.
And that leads in to another big issue. Like the first movie, there was no character depth or character growth. I didn't care about any of the characters (except those from the first film). I didn't really even know their names or anything else about them. There was no personal connection to anything happening to any of them. It was just pointless death after pointless death.
And the characters they did spend time on were so horribly acted that you didn't like them anyway. I'm not even going to point out specific characters that were over-acted... because they all were (with the exception of maybe two... which were the teacher from the first film in one short flashback, and Noriko, who has one short scene at the end). I also didn't like how Shuya was portrayed in the first film, and that pretty much carries over to this one, as well (he's still more awkward than anything).
A couple other notes: The cinematography and the music were both really good; the ending was just dumb and silly; and don't even get me started on all the plot holes (and I'm very rarely one to pick up on plot holes myself). And they could have told us where the hell Noriko was for the entirety of the movie instead of making us wonder the entire time. So yeah, the movie had a lot of good ideas, but it ultimately fell on its face (hard). If it were to be altered and done in book form (though I do think that was done to some degree for a manga sequel), I believe it could be really good. Too bad that for now, it's really not.