
Included was this advert:

Here is the official web page of the game: http://www.konami.jp/gs/game/deathnote/ - specific info on the game: http://www.konami.jp/gs/game/deathnote/game01.html
Apparently you have to find out who is who, you don't know from the characters who is L or who is Kira (they are not the same as in the story). You can choose to either be Kira with the intent to find out and kill L or to be L with the goal of arresting Kira. Throughout the game you try to gain trust from the others and consequentially get information.
However, there doesn't seem to be that much more info out so I can't say much else about it. Just letting those interested in the game to know about it. Sorry if this is old news, I don't seem to see any topics about it yet.