Death Note asks a very uncomfortable question and refuses to answer it for you. A bored student finds a notebook that kills anyone whose name he writes in it. He decides to use it on criminals. Somewhere in the following weeks he stops being the protagonist and nobody quite marks the moment it happened.
The genius of Tsugumi Ohba's writing is that the show is almost entirely people sitting in rooms thinking. There is no action. The tension comes from two extremely intelligent people trying to make each other flinch, and from the fact that both of them are right about the other and wrong about themselves.
L is the reason it works. He sits wrong, eats nothing but sugar, and is the only person alive who guessed correctly within days. Their mutual respect is real, which makes what happens between them worse.
Ryuk floats above all of it eating apples, providing commentary, and reminding you that from a shinigami's perspective this is just entertainment.
This collection covers Light, L, Ryuk, Misa, Near and the notebook itself. Install one and try not to write anything down.