Saw the movie last night. To my knowledge the Cruise role is totally fictitious but the lead Japanese warrior is based on a man who was a leader among the Samurai who did oppose the extreme efforts at modernization, and who is known for being one of the few who did learn English. Yes, it is hollywood movie with the romantization that usually comes from that source, but I feel that it did reasonably cover the credo of Samurai and is a decent depiction of the time and place.
Some online reviews come down harder on the historical imprecision. The only thing that really bugged me was the total absence of any flavor of Japan in the soundtrack.
In my mind this tune was playing as they rolled credits:
Heisei Ishinn by King Giddra
Another contemporary Japanese tune with traditional elements is Izumi by Uzi
Those are direct links to mp3 files that are about 4mb. a bit big if you are on a slow or dial modem connection.