Rhythm games have always transcended nationality, though. Rhythm is something that can be learned without complex theories; it just takes practice and repetition. This is true for children, adults, men and women. This is why I thought a worldwide release of this title wasn't just a pipe dream.
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I think there will be increased potential for game music to cross over into the mainstream in the future, but avid fans usually don't respond to gimmicks they feel are too contrived. The key is to start with as pure a game concept as possible, and give it the type of music that suits it best. If the fans respond well as a result, performing the song live in concert would be a natural next step. That sort of pattern seems ideal to me.
I was rocking away at RH quite happily this week until I hit the level with the off-beats, and now I'm stuck. Here's a Japanese trailer with examples of many of the mini-games within Rhythm Heaven.