Shamo is one series that is difficult to write a simple review for, but I'll try to keep it brief. I may as well get it out of the way - Shamo has one of the worst endings to a manga series that I've ever seen, There's no resolution, no ultimate lesson, just a strong feeling that the author wanted the series over and done with. Now, there are plenty of mediocre manga series but it is particularly distressing here because of the way Shamo started out. The first several volumes or so were cerebral, dark and well-paced. It took a lot of risks, giving us a main character that was clearly a villain, but who the reader is compelled to root for. This is done by giving the reader a clear look at how he got to be where he is and how he feels during the whole process. It gives us a look at the less savory elements of Japanese culture, but the themes are fairly universal. One of the central themes is how society can never really forgive a criminal and often perpetuates their unlawful behavior because of it. What we get is a character study of a person completely shunned by society. While he is intelligent and talented and desires recognition, his experiences and bad decisions continue to haunt him and prevent him living a rewarding or even a normal life.
That's why I need to give this manga a good rating despite its glaring flaws. The latter half of the series really begins to lose track of what the story is about. The last few volumes are a complete waste of time. Those that have followed the series know about the long hiatus it experienced. It was stuck in a long, messy lawsuit where the creators fought over ownership. In the end, it's understandable how the series ended up but no less disappointing.
I still recommend giving it a read. Just don't bother reading after the first half or so.