I bought this comic and read it as a friend recommendation, because I'm a fan of Batman, but not to the extent of buying any of his comics. But as my friend said that "this must be the comic used as inspiration for Batman: The Dark Knight movie for how the Joker is depicted" (and that is my favourite Batman movie by far), I couldn't resist reading it... And yes, this must have been the inspiration.
An apparently "cured" Joker is released from Arkham Asylum and, as you would expect, soon starts to wreak chaos at Gotham, especially to the criminal organizations. In fact, Batman appears just in the last pages, the whole comic is dedicated to the clown arch-enemy. And how well it is represented: pure chaos, dementia, craziness, violence for the simple reason of violence itself, revenge... a madman that can't be bargained or reasoned with... A Joker that just wants to create chaos, and enjoys causing it.
We also have a dark and decayed Gotham, with some classic enemies ruling part of the city's underground activities, and no clue of how is Batman going. The drawings and specially the painting give the comic a creepy look, and both language and images are not for children. Kills, tortures and sexual related acts appear.
Also, the title is very appropriate: Batman is a secondary character. The narrator isn't the Joker either, though.
A must read if you enjoy Batman comics, and x2 if you also enjoyed the 2009 movie.