The 690M released was obviously a bothched/fake release. All the comments at the torrent portals were negative on it from the beginning. Since the game content is 99% music data that's already digital and compressed there's no way it's gonna compress down to that size. You've never seen any other rock band or guitar hero title anywhere near that size.
However..... at 690M i had to download it and give it a peek myself too...... hehe
However..... at 690M i had to download it and give it a peek myself too...... hehe