One of the strengths of the Batman character is that he is open to multiple interpretations, ranging from the campy to the psychotic. Here Morrison gives us a Batman who questions his own sanity and seems to get swept up in the madness of the Arkham Asylum inmates. This is a version of Batman that would not play well in mainstream superhero comics but within the context of this story it works.
Dave McKean's art is justly praised, but I find myself wondering if the story would work as well if rendered in a more realistic style. I suspect that divorced from McKean's shadowy abstract art the story by itself would be considered bizarrely out of character for Batman.
Letterer Gaspar Saladino gives each character a unique font style which is very creative, but between the coloring and the messy style of the Joker's lettering I found it difficult to decipher what the Joker was saying. Maybe that was the point.