The manga kicks ass. I haven't seen the anime yet, but the first volume is due on DVD in November.
If you like a suspenseful story that keeps you glued to your seat, this is the series to check out. Basically, the story is about a guy named Light Yagami who gets his hands on a supernatural notebook that can kill people. Of course, he decides to use it to cleanse the world of criminals and ends up with investigators on his trail. However, Light is possibly the most clever bastard I have ever seen in a series and finds interesting ways of keeping them in the dark. If you like a story that keeps you guessing, with depth, supernatural death-bringers, cool characters, suspense and action, Death Note is the series for you.
'nuff said.
EDIT: I wish I had the music from Reading Rainbow....y'know....the one where the kids talk about their favorite books and then the music goes "Duh duh duh!"