I downloaded Sengoku awhile back, and I'd have to say it is a very historically accurate version of a Japanese historical based RPG. Sengoku is of course, the Time of War. Prior to the Shogunate when this generalismo provided an iron handed central rule of Japan there was century of constant war between various noble houses, clans, and struggles to place different emperors on the throne.
Unfortunately, my players are fantasy based gamers - they like magic and monsters, more than historical gameplay. So I never could find a group to play Sengoku.
As far as fantasy based Japanese-esque RPGs go, Legend of the Five Rings is popular, though I hate the map, or at least the concept of a land-locked (more like China) Japanese empire. Much of Japan's unique history and culture is derived from the fact that Japan is an island nation. Separated from outside influences by at least the Sea of Japan.
On the same hand, I've never cared for Oriental Adventures, especially since WotC licensed the L5R Rokugan world map - eck!
As an aside, parsing out the name Rokugan (roku is Japanese for the number six.) What does six or Roku have to do with five rings?? "Go" is number five in Japanese, not that they should call it "Gogan", but steer away from vocabular usage to suggest the number six has anything to do with anything.
I agree, though if you want to play an historical Japanese setting, Sengoku is probably the most accurate available. Although the game mechanics rules in Sengoku allow for the katana fights against large odds, like you'd find in Japanese adventure movies - so there's a bit of fantasy element in the game play as well.