Before watching the movie I looked for any kind of Internet reviews, as I usually do, and what I found kind of surprised me, since they were VERY low ratings, like Metacritic's. It was disappointing at first, because I was really looking foward to watching it, but since I love oriental/yakuza themed movies and had nothing better to do anyways, I decided to give it a chance.
For starters, I enjoyed it a lot! It's not by any means a masterpiece, but it was a very solid movie with good casting and good plot. If you are into the japanese culture as I am, I can guarantee you are going to have a good time as well. Maybe because my expectations were set very low (by the reviews and ratings) I ended up enjoying it more than I thought I would.
The acting is very convincing and even though Jared Leto's character doesn't talk much, I believe it was the author intention to give him this blank and mysterious background. The other, japanese, characters are also very well portrayed, but not much development is given into them. The post WW-II Japan's atmosphere is amazing, and it does give you a feeling about the underground yakuza world at the time.
For what I think could have been better, the pacing was a bit too slow at times and the story is VERY predictable once you figure out who the bad guy is. It could also have developed a bit better our main protagonist, I understand he's supposed to be mysterious, but almost NOTHING is given to us about his background or anything that could explain why he acts the way he does throught the movie (maybe a sequel exploring it, who knows?).
Nonetheless, it was a good movie and I strongly advise you ignore the critics and go watch it for yourself and, hopefully, help spreading the word afterwards too!