I loved it! With a premise this ridiculous it's easy to sound hyperbolic because "it shouldn't be this good," but this book, on top of executing spectacularly on the premise, is also a very good Batman comic. It plays in the world of Gotham City and never apologizes for that. Lee Weeks is a perfect fit for noir Batman stories and this is one of the best I've seen in a while. The only complaint I really have is that this is not a good first Batman book. It relies on the reader the finer points of Batman's gear in order to suspend their disbelief. When Fudd shoots Batman with a shotgun TWICE, it's a little strange that they don't mention how or why he survived. Obviously Batman fans can assume his kevlar reinforced symbol and cape are why he survived, but the new reader might just see Batman as being bulletproof for some reason. It's a minor quibble in the grand scheme of things, but it is an issue.
Overall the book is fantastic. The mood is just right, the pages are paneled expertly, and the Gothamized Looney Tunes characters are a treasure. If you read one Batman comic this year, let it be this one.