The movie picks up where we last left off. Raito is invited to work alongside L and a small task force. This gives Raito/Kira a unique insight into all what is happening to catch him. What happens next is that there is a NEW Kira in town, killing people to get into contact with the original Kira. This new Kira has even the gift of the Shinigami Eyes (basically you can tell people's names from looking at them).
The cat-and-mouse game begins again between Kira and L, but it has a unique twist.
The movie still follows the manga rather closely regarding overall plot. The ending, however, had even me shocked. Eh rambling on about the manga which contains minor spoilers I guess >.>
Considering the manga has 12 volumes (+1 extra with information), the two movies span around 7 volumes which I think is more than enough. So just saying if you're interested, there is more to the story.
As I said, the ending was surprising, but well done. As in the previous film, this truly is a battle of wits, and you cannot wait to see who wins. It'll spur a debate as to whether Raito was right or not. Just as in the movie, you've got people who are for Kira and are against him. You'll feel the same. And for that reason I also give this a 5/6, even though I found this movie better than the first part.