Death Note starts on a simple principle, Light Yagami, perfect student, finds the power to control death, but soon becomes a complex story as different plot elements and character motives intertwine; suspicious as to the sudden outbreak of deaths, the world's top detective, known simply as "L" is hired to investigate the case. L's presence becomes a constant source of antagonism to Light (now under the alias of Kira) as he tries to maintain his plans of making the world a better place while avoiding suspicion from those around him. As the series branches out, more and more characters are introduced to keep Light on his toes in his quest to create the perfect Utopia; the fun part of this is that, all the while Light Yagami is kept on his toes, so too are we as readers - the series has a great ability to draw you in and not let go.
Other elements that I personally enjoy are the supernatural tones of the story and the way that it can, even through the dark issues contained, rouse humour; it's hard not to laugh at the black humour contained when Light's sister vents her hate for Kira, while Light himself cooly agrees. The art itself is also amazing, every single chapter is drawn beautifully.
When I finished the first volume, I was suspicious as to how Death Note would be able to sustain itself over so many different chapters, now that I have just finished the sixth volume, I can, so far, say that it has not failed to deliver. Out of those that I have read so far, I would say that number IV is my favourite, though I would class every volume I have read as essential reading for the manga fan.
I am eagerly awaiting the delivery of the seventh and eighth volumes as I type this! I was introduced to the series by a friend who has since got another two friends hooked - it really is a great series to get into; get yourself hooked!