The story and characters is the best part of the game, and of course the mini games. People get put off thinking it will be a Japanese GTA, when it is not. Thats why many thinks it mediocre. The game is like Shenmue but with more focus on fighting.
Personally I think its one of the strongest series, with characters you just want to see more of. Yakuza 5 must make it to the west, its the biggest Yakuza game yet. And I think it would increase the fanbase. Securing the future sales of Yakuza titles on the PS4.