Of all the Rifts World Books I own I would have to say the one I like best is Japan. I'm not going to say its the best written or the best book overall. Merely that it is the best book for my style of game. Japan can be a difficult play to write about. Its a mix of old and new that doesn't exist much outside of Asia and its not something we Westerners always grasp at all well. Rifts Japan does (for the scope of the book) a fair job of trying to make the Japan of the Rifts setting to be consistent to itself at least.
Never trust the dice