I've only just watched this and found there are 3 threads about this show, but thought I'll post here as has most comments 
So not read the book or seen any earlier version, and quite honestly did feel it would have been better without the english man have a featuring part.
But certianly whether through acting skills or being himself (joke) conveyed that yes his culture did make him a "barbarian". And him learning to be a bit less "barbaric", think a bit more, etc., was interesting but a bit laboured.
I have no idea whether what was shown is an accurate representation of Japanese culture at the time but found it intriguing, and I was always slow to grasp the plot twists, or rather manipulations that were going on.
I wonder how it would have been just to have had it shown purely from the Japanese perspective, in which occassional Europeans intervened. Maybe if there is a second series it will.
But found the landscape (and the weather), the sets for smaller communities as much as larger cities fascinating.
Although, as with Giri/Haji, I just didn't grasp much of the sentiment and culture. So supect I am unfortunately closer to Blackthorne ie having most of what was going on passing me by.