Started playing today, and I haven't really let up all day. Really enjoying it so far, the rooftops and underground of Kamurocho is really well implemented.
Not sure what else to say, it really does feel similar to Yakuza 3, but at the same time has a lot of really nice improvements (The levelling up system in particular sticks out). Been looking out for side missions too, finished all of Saigo's training missions which were interesting.