The American manga market, you may have noticed, is dramatically different from the American novel market. Aside from the obvious (manga have pictures, novels generally don't,) there's the matter of "classics." Novelists like Twain, Vonnegut, and Austen have been selling like hotcakes for ages. The manga market is a lot younger, and series fade in and out of vogue more quickly. Only a few titles from the early days are still in print, much less popular.
So when a manga series manages to stick on bestseller lists two years after the final volume's release, you know there's something good going on.
That goodness is Death Note, the story of a young man who finds a notebook. He discovers that anyone whose name is written in the notebook will die, and begins using it to pick off killers, crooks, and thieves - and anyone else who gets in his way. Tsugumi Ohba weaves together one heck of a psychological cat-and-mouse game, helped along by Takeshi Obata's gorgeous, insanely detailed illustrations.
It's all very Dexter, but with a lot less relationship drama and a lot more ink.