NOTE: I'll probably come back to this review at some point and edit my scores to be a bit more realistic, but I just finished binge-reading this comic and I'm still spinning from the crazy-ass wild ride I just went on.
TL;DR - This has got to be one of the better mangas I've read in a while. I have a lot of 5-star mangas in my reading and read lists, and they're all rated highly because they're very entertaining, well-drawn, etc., but this one is on an entirely different level. It's gut-wrenching, sad, satisfying, angering, etc., all in one. It's one of the few mangas that's probably made me feel every emotion I can think of feeling, and it's one of the very few things out of all mediums (manga, anime, video game, anything) that's made me think about my own actual real life.
It's not a light-hearted read, and it's definitely not for someone looking for happy-go-lucky, funny romance. Be advised.
STORY - The story overall is very good. The buildup of events and how everything ends up tying together is done quite well, although there were (VERY occasional) sparse dots of plot convenience here and there. The games they end up playing are all very interesting and very creative. Because of how unique some of the games are, it's actually a fun read for intellectuals in terms of devising strategies for winning. But at the same time, it doesn't go hardcore genius-strategist on you either, so it's still at a level where non-chess champions can understand and enjoy it. Alongside the character development, everything simply builds very well.
ART - Art is great. I never felt like at any point any of the characters or buildings/props were badly proportioned, and shading work as well as level of detail is excellent. I think the only other manga I've seen that is nearly or as good is probably Grand Blue Dreaming (which you should check out purely on the basis of artwork, by the way).
CHARACTERS - The main characters who were important were done pretty well. They had great back stories and you get to really, really know the characters and understand their mentalities and their reasons for their choices, which is something many other stories, animes, manga, and multimedia in general sorely lack. Characters don't do evil shit "just because", and that's really refreshing in the world of shounen manga. I also want to comment that it was a little weird to me how this was in the Shounen manga category, as I certainly feel it would have been slightly more appropriate in seinen. But whatever. My only beef with the characters is that there are a few here and there that didn't have the same depth and level of attention as others, and although you obviously can't have 20 main characters, it is my opinion a few of the ones the author decided ignore needed the emphasis.
OVERALL - A highly enjoyable read. It's one of those ones that keeps you clicking the 'Next' button over and over until you realize it's 3AM and you have work the next day. If you like mangas that have lots of action and violence, lots of examination of the human condition and what it means to be alive, lots of relatable characters and great plot development, this manga is for you.