Brother may seem like a whole lot of meaningless gore, and in fact I don't think it was a particularly well-made or enjoyable movie, but it provides valuable insight into the Japanese perception of their place in the world. I'm not sure this was intended by the director, but it makes a very interesting contrast to, for example, "Rising Sun", another fairly average movie (can't comment on the book, haven't read it), which showed a very American perspective of the Japanese.
Whereas in Rising Sun, we saw the Japanese as sneaky little yellow men hiding their prejudices, corruption and kinky sex behind polite smiles and a facade of high culture, here Kitano portrays them (or at least the Yakuza) as noble, loyal, selfless, brave warriors, willing to sacrifice all to protect their honour. Quite a contrast!
Rising Sun showed Westerners (represented by the US alone, as usual) as passionate but ultimately rational, independent-minded for the better, and, for the most part at least, genuine (in a "what you see is what you get" sense). Kyoudai (incidentally, the title refers not to any blood relationship between the two main characters - there was none!, but to the "brotherhood" of the Yakuza) shows Westerners as emotionally out-of-control, intellectually lacking, hopelessly disorganised and incapable of any subtlety or restraint. From considerable experience in Japan I can assure you that this is an accurate representation of the stereotype held by many Japanese.
Another (I think) accurate representation of the Japanese mindset in this film lies in the ease with which the Japanese muscle-in on the US underworld. With their diligence, their capacity for cooperation and self-sacrifice towards long-term, collective goals, how could they possibly fail against this disorganised rabble of Westerners?! - this is the attitude presented, and mostly validated in this film. It's very interesting, then, that the "brotherhood" are ultimately unsuccessful in their power-bid. Is this a symbolic recognition that the US has remained militarily and economically supreme? At the least, I feel that the way in which Kitano's character dies again reflects an important facet of the Japanese mindset, being the attitude that there is only ever a choice of complete victory or total failure, conquering the whole of Asia or being stripped of all military power, scoring highly in the University entrance exams or dropping out of the academic world completely - there is absolutely no room for compromise or mediocrity, and thus a willingness follows to sacrifice everything in the bid for that absolute, and possibly elusive, victory. Of course, this has alarming implications for Japan's potential return to military and/or economic power.
But if you want, you can forget my interpretations and just see this movie as a whole lot of meaningless gore.