As a fan of the Yakuza series, and having played all the mainline entries and available western spin-offs, I can safely say that this is my favourite video game series of all time.
Gaiden is a relatively short chapter in the long running saga, and aims to bridge the gap between Yakuza 6, Like A Dragon, and the upcoming Like A Dragon Infinite Wealth.
The story here is standard fare if you’ve played the other Yakuza games, but slightly weaker due to its shorter length. In exchange, there are some new innovations here that bring something fresh to fans of the series.
The Akame side quests are a fun diversion (side quests are a draw by itself in the Yakuza games) and provide some structure to them. You also get to explore a new location called The Castle, which has an extensive Battle Arena game. This is extensive and could almost be a fighting game by itself. You get to collect fighters and level them up, almost like a sim management game wrapped inside.
If you’re a fan of the series already, playing this is a no-brainer. It whets your appetite for the upcoming sequel. However, if this is your first entry point to the Yakuza series, start with Yakuza 0 and play the entire series from there. You won’t regret it.