I really had to push myself to keep reading after a dozen chapters. I don't know, it just falls into a pattern and it isn't exciting enough to justify holding off character development for later. The main character isn't likable enough. He's got a dark past but it's revealed too early without any leaving any mystery and he's not charismatic enough to make the most of it. He's not cool enough to make his confidence seem anything other than arrogance. He's 21 but looks like an ordinary high schooler which makes him seem rather bratty. His lack of appeal makes his hunt for revenge seem petty rather than captivating.
There's nothing really wrong with the art, it's just that Kurosaki's character design is too plain and everything looks so shounen-like.
Despite the premise, I didn't find this manga dark at all yet there isn't any comedy either. It's trying too hard to please a wider audience when it would have done better to be darker and edgier.
I'm surprised at the high ratings. For me this falls flat despite its potential.