Yakuza 4 is in kind of a weird spot for me, it does solve many of the problems 3 had like the bad combat and clunky movement, graphically it also looks surprisingly better too, but despite all that I felt that 4 was a fairly unremarkable entry.
It does add for the first time in the franchise multiple playable characters, each with its own fight style, but it doesn't really do much else. For the first time since Yakuza 1 there's no other area besides kamurocho, and while kamurocho has been expanded by adding roofs and hallways they don't really do much besides providing shortcuts (that I personally never used) and maybe having a couple of substories that require to go there.
The plot is kind of a mess even for yakuza standards, I appreciate that they tried to intertwine 4 different stories, but it does become almost comical towards the end with the amount of twists and betrayals that it crams in like 20 minutes.
Overall I don't think that Yakuza 4 is a bad game, I enjoyed my time with it and I would recommend it to any fan of the saga, it just left me feeling kind of cold despite introducing some of the most loved characters in the franchise for the first time.