I read this book purely because I'd seen so many references that The Hunger Games was a Battle Royale ripoff. Given that the whole idea of sending a "tribute" of youngsters to fight each other, or some monster, until there's only one survivor goes back to at least the Greeks, and that there's nothing else that's really similar between the two books, I'd rather think that Battle Royale is a 1984 ripoff. No, 1984
didn't involve a teenage deathmatch, but the Greater East Asia of BR is certainly very much like the nations of 1984.
The biggest problem with Battle Royale is that it's Japanese. Now, I don't have a problem with Japanese stories, and it may work very well in Japanese, but personally I think the translation is horrible. The language may work wonderfully in Japanese, but it's either been translated incorrectly or literally - and as far as I'm concerned, literal translations are just as bad as incorrect ones. If you want to translate for an English audience, use idiomatic English.