Yakuza 1
With the fifth major numbered installment in the Yakuza (Ryu Ga Gotoku) series about to be released in Japan, Sega have chosen to release four digest videos for the series on their Youtube channel. While these are all in Japanese and the game hasn’t even been confirmed for release internationally yet, this may give you an idea as to what the games are about if you haven’t played them already.
Yakuza 1 and 2 were released internationally for the Playstation 2 while 3 and 4 were also released internationally for the Playstation 3. Each of the games since Yakuza 3 have come with digest videos included with the game and it is strongly advised to watch them if you have not played earlier installments. All games since Yakuza 1 have been released only with a Japanese dub.
Yakuza 2
Yakuza 3
Yakuza 4