Wait, really?
Yakuza 0 was my first Yakuza and I adored it. But a large part of my excitement about the series was based on the assumption that Y0 followed the universal rule that prequels are worse than at least some of the other entries. Is everything going to be downhill from here?
The best in the series for 2 reasons.
One, it went back to the Yakuza 1 style of a VERY grounded story that doesn't really go too insane or have any unbelievable moments. The entire story, from start to finish, maintains the same level of quality. Yakuza 2 is perhaps the only other Yakuza game that has a comparable story with incredible highs but even that has one or two moments that some might find a little unrealistic.
Two, Yakuza 0 is the culmination of TEN YEARS of working on the Yakuza franchises, and around 6 years of working on the hardware of the PS3. I don't know if you know this but asset reuse is a key reason why Yakuza games maintain the level of quality that they do. I mean hell, some of the heat moves are moves that were recorded with motion capture for Yakuza 1 and Yakuza 2, PS2 games.
The only Yakuza games that have stories I would consider BAD, were Yakuza 5 and Yakuza 3. In the case of yakuza 5, it's the ending that screws the pooch but the individual chapters are fantastic and hella fun, and in the case of Yakuza 3, it's a bit weird because while that game does have some of the lowest lows story wise, it also has some of the highest highs.
There was a particular scene in Yakuza 0 that brought a tear to my eye, but only Yakuza 3 made me straight up cry with one particular scene.
All the Yakuza games are great games, and definitely worth playing. There's not a single Yakuza game that I've played that I felt like I wasted my time or that it wasn't worth playing. They're all excellent. Yakuza 0 just has the advantage of having a lot of the "legwork" already being done for it.