The beauty of Death Note (manga, at least; can't speak for the anime) is how FUCKING AWESOME a mystery story it turns into. If you read the manga, past the first few chapters to where Light starts to get himself in too deep, watching Light and L go back and forth playing the fool on each other and try to stay one-up really gets you hooked. It's really hard to just stop partway through, you just want to keep reading even though it totally scares the shit out of you. It really is just about the most fucked up thing ever, and you don't want to keep reading, but you can't stop—kind of like a Stephen King novel, only a hundred times better.

And by the way, the live-action movies are also a whole other level of amazing.