Just recently read it and loved it. Not the best Batman Elseworlds story ever, but I simply LOVED the premise, the concept and the atmosphere.

Gordon as a hard-boiled Chandler-esq private eye is a truly brilliant concept. Gotham really is a natural setting for noir storytelling. And though we barely get to see him, I loved the depiction of Batman here. It really dug into the 'urban myth' aspect of the character more than any other iteration - and that's before you get into a certain mindscr#wing 'twist'...

I also loved the depictions of Harvey Dent, Selina Kyle, Boss Zucco and Jack Napier.

spoilers:
Now, as far as the ending goes, I have mixed feelings. On the one hand, the notion that Batman in this verse is an actual urban myth, invented by Harvey Dent, and that Gordon's fractured psyche imagines him, is a mind-numbingly brilliant one. But I feel that not enough was done to build up or foreshadow this reveal...and we barely get any time to chew upon it since its literally in the last panel. Though I also kinda like the ambiguity of it. But I actually felt that this story could serve as a good 'origin story' of sorts, had Batman been real and Gordon not died. We could have seen a set-up of the classic status quo, albeit in this more noir-ish world. But then I guess it wouldn't have been much of an 'Elseworld'...
end of spoilers