First off, if you have no patience for cult movies, with questionable production values, unknown actors, and absurdist plots, then you'd be better off skipping Battle Royale. The plot seems like the thinnest set-up for exploitation: in the near future, beset by intractable discipline problems in Japanese schools (probably the fact that they started acting the way American students do now), the Japanese authorities somehow decide that the ideal solution is to randomly pick a Japanese Junior High School class, transport them to a remote island, give them all a random weapon, and allow only one to leave alive. Go!
Certainly not the first film to go there (set the wayback machine for The Most Dangerous Game to see an early, and also worthwhile, exploration of this idea), Battle Royale has several unexpected things going for it. The Battle, which is an annual event in the film, is an eagerly covered media event, depicting with indicting accuracy the hunger modern media exhibits for a youth-oriented bloodletting (and this from a film which was conceived before Survivor conquered American airwaves). Japanese super-actor of the 80s Beat Takeshi plays the organizer of the Battle, and we keep cutting back to him on the cell with his family, showing that his need to enforce discipline in the Japanese classroom by force doesn't extend to his own domestic environment.
In order to keep the action moving (after all, you need to keep seeing student casualties for this type of movie to move forward), random sections of the island are bombarded on a continually updated schedule. This keeps the students scrambling from station to station and becomes the 'ticking clock' driving action towards a climax. Surprisingly, the ending plot variations take us to back story we wouldn't expect in a cult film.
While Battle Royale can move into highbrow artistic commentary, those elements are the dessert topping on the foundation of a fine cult film. If you have any weakness for those, put finding a Region 1 DVD of this (or a Region 2 DVD player) high on your list of priorities.