Ryu ga Gotoku Zero has the best music in the entire Yakuza franchise; none of the other soundtracks are even NEARLY as badass~ I may be a girl, but I can't stop falling for macho music like this.
...Also, Takaya Kuroda (Kiryu) sounds like freakin' Dracula even with his normal voice. He needs to play someone in One Piece so bad (apart from Bogart). Maybe Kaido? (Though Tessho Genda would be even better.)