Deeply intelligent and devilishly inventive, Death Note is arguably one of the smartest and most cutting-edge shounen titles out there, and while it is a shounen title it pushes into seinen territory with its maturity. This is not a battle manga, despite appearances. The plot of Death Note is rich and dense; though it can be overly explanatory at points it manages to pack a huge amount of plot into a relatively small space.
Death Note lives and dies by its plot twists. It basically reinvents itself with every new volume, delivering one staggering plot turn after another. Keeping the reader on the edge of their seats is one of the things that this manga does best, and one of the reasons why it's so popular.
The artwork is overall very good. It's a blend of stark realism with gothic fantasy elements, the latter of which is most apparent in the cover art.
Another very strong point is its diverse cast of extremely memorable characters, many of which have large fan bases among anime fans. Ask any otaku about Light, L, Misa, Near, Mello, etc. and the responses will be varied, but nearly all of them will respond with recognition. The popularity of these characters rival those of, for example, Naruto, the protagonist of one of Shounen Jump's highest grossing animes ever.
People like and dislike the characters for different reasons, however. One thing that Death Note does that many other stories are not able to do effectively is make every single character likable and flawed in some way. Even the main character, Light, who can be easily viewed as a cold and heartless serial killer has a personality that people can empathize with. In fact, he is one of the most popular anime characters of all time. Some people absolutely hate Light, but like other characters, such as L, for different reasons. Death Note never tells you which characters you should like and dislike, or which characters you should root for, it lets you decide it all on your own.
One very interesting thing about Death Note is its view of morality. None of the character can be viewed as good or bad, justice or injustice. The two main opposing forces in this manga are just two people with strong senses of justice and very different ideas of how it is to be carried out. The main character can very easily be viewed as the bad guy, because although his main intentions are righteous, he has a very brutal and methodical way of carrying them out. The antagonist can be looked at as the one fighting against evil, but the methods he uses are questionable at best; he becomes obsessed with his search and is willing to do nearly anything to reach his goal regardless of the ethical questions surrounding it.
Because of this obscure view of ethics, Death Note has been pegged as a twisted and murky morality tale. However, the psychological aspects are obviously very well thought out and meant to cause you to try and decide who the good characters are, who the bad characters are, and whether or not there really is such a thing. It's up to you as the reader to decide who's right and who's wrong; the decision is never made for you, which is something that makes Death Note so much deeper and thought-provoking than most manga, or most books for that matter.
I read somewhere that in order to enjoy Death Note, you need to be a little twisted, but most anime fans are. If you like anime at all, there is absolutely no excuse for not reading this manga. It's one of the best of the best. If you haven't ever read a manga before, this might not be a good first choice because it's deeply psychological and takes a lot of paying attention, but Death Note is a force to be reckoned with in the world of manga and shouldn't be passed up by anyone who likes dark morality tales.