The Yakuza series is a set of narrative-driven games about Kazuma Kiriya, a Yakuza member (the Yakuza is the equivalent of the Mafia but in Japan), during his Yakuza days and post-Yakuza days. Set in the fictional Kamurocho district, in Tokyo. You go around cities doing events, which include fighting, an assortment of minigames, and a lot of cutscenes.
The Yakuza series was created by Super Monkey Ball creator, Toshihiro Nagoshi. It started on the ps2, and had a casual amount of releases on there and the succeeding console. Yakuza 1 & 2 were released on the Playstation 2. Yakuza 3-5 were released on the ps3. so that brings the question: if only a few Yakuza games were released on previous consoles, why then, can i play several new yakuza games on my ps4 along with the rest of the series. Yakuza 0, a prequel to the original Yakuza was released in 2015. Yakuza 6 was released in 2016. Yazuka Kiwami, released in 2016, and Yakuza Kiwami 2, released in 2017, are remakes of the first two games. A spin-off, Judgement, was released in 2018. The remastered collection, containing all ps3 Yakuza games (3-5) was released in 2019. The final game on ps4, Yakuza: Like a Dragon, has not been released in the west yet but it has released in 2020, in Japan.
This brings us to the main question, why do i own all of these entries (except the one that hasn't released in the west). It's because they're good and i enjoy them.