Darker than BLACK is an amazing anime, it's one of my top 3 anime! The storyline, the plot, the ending, it's all made perfect. The balance of gag and seriousness is also made well.
But it would've been nice if there was more parts with Li Shengshun in it, I liked his change in personality whenever he goes undercover, I also like it when he interacts with normal human beings.
The mangaka's used of high speed action keeps you on your feet, you never know where it leads to and it is very unpredicatable.
The seiyu for this anime were also well done, of course, like any other anime, the Japanese version was done better.