A Rockstar spokeperson in an interesting interview to Kotaku has said that L.A Noire isn't complete yet.
The spokeperson was asked whether the release of game's final announced DLC content "Reefer Madness Vice Case", completed the game?, to this he replied, "The game isn't complete yet"
Rockstar has released a total of five DLC cases for L.A Noire. Did the game will see many more cases? well now we all have seen Rockstar's answer, so just wait and watch.