Being one who has played four of the Yakuza games, or Ryu ga Gotoku, series, I guess you can describe it as being a Japanese Grand Theft Auto in a nutshell. However, I am not too familiar with the PSP spin-off, though I think it is the same or similar.
As for the girls, there's a part in the game where you are able to visit a hostess club and in this part, you can get to familiarize yourself with the hostesses by answering or giving the right responses; have a conversation, take them out on a date, go bowling, golf, etc. This is where Tonooka, Endo, and Tachibana come in with their voice acting and their face CG. Can't wait!