Officially, this is considered the final book in the Death Note series. However, it's really more of a companion book than anything else. Not that that's a bad thing at all. In fact, it's nothing short of awesome.
Within these 200-odd pages, you'll be treated to all kinds of goodies.
For starters, all the unresolved plotlines (especially the fate of Misa) are addressed. You also get every single piece of Death Note trivia that you would possibly want to know. So not only do we finally learn L's real name, we learn everything he ever ate during the course of the seires (Oh boundless joy!). Also, perhaps to give us a break from how serious the series has been, many of the characters pop up occasionally and break the fourth wall by providing some amusing commentary of their own. At least one even comments on their own in-series death.
However, as good as all this is, there are two places where this book really shines.
First, a lot of this book goes behind the scenes as Ohba and Obata give us a satisfying peak at their creative processes. My favorite part was where Ohba talks about where he got the idea for EACH chapter title. Man, this guy gives a whole new meaning to the term "detail-oriented".
Second, this volume wraps up with the series' pilot chapter, aka the FIRST Death Note manga ever written. It has the same basic concept as the series (a deadly notebook), but takes it in a more "Stephen King-ish" direction. Also, other than Ryuuk, it stars a completely different cast of characters. That said, one of these "newbies" bears a striking physical resemblance to a certain, insane prosecutor-turned-Kira-worshipper. If you're a fan of the seires, you probably know who I mean. Like the series, the pilot was a great read. In fact, I think it would make a great movie (much easier to adapt than the series, I'd think).
The only negative thing about this book was that, on 1 or 2 pages toward the end, Misa was even more exposed than usual. I wasn't quite expecting this and it made me feel somewhat uncomfortable. However, this really isn't enough to cost it a star. It's just a few pages; easy to skip over.
This is highly recommended for Death Note fans who know when to stop taking things too seriously.
Also somewhat recommended for Stephen King fans or Horror fans in general (due to the aforementioned pilot chapter).