People who think that THE LONG HALLOWEEN is the definitive Two-Face origin seriously need to reread the book. It's not even a good Two-Face origin.
LONG HALLOWEEN is a deeply superficial book, more interested in misdirection and splashy empty action scenes than actual character and psychological depth, which may not be important for all characters but is essential for Harvey Dent. It spends far more time on horribly cliched dialogue, oblique references to the Godfather, and a murder mystery that just absolutely makes no sense (I could shoot holes though ______ being the killer for hours) than devoting anything more to Two-Face's origin than the following:
"Harvey is a good guy. Harvey is angry. He's now Two-Face. The end."
It goes no deeper than that.
I'm convinced that if Tim Sale hadn't been doing the gorgeous, gorgeous art, no one would care about LONG HALLOWEEN. Try to imagine it without Sale's art, and imagine if you'd still be interested. Maybe you would, but I bet many, many would see right through that painfully mediocre script. (Here's a fun drinking game: every time Loeb uses an ellipsis, take a shot! You'll be wasted by page three)
Honestly, do you want the true definitive Two-Face origin? Seek out BATMAN ANNUAL # 14, "Eye of the Beholder," by Andrew Helfer and Chris Sprouce. Not only did LONG HALLOWEEN ride its coat-tails just as hard as it did GODFATHER and YEAR ONE (right down the Harvey's assistant Adrian... oops, I mean Vernon Fields... groan), but it told his story with far power power, depth, weight, and tragedy. It's such a shame that it's not in print. It should have been included in the upcoming TWO-FACE TPB.
While Mr. Sable is not approaching Harvey the way I'd ideally like to see it done (or do myself), I applaud him for doing something decidedly different and unique with the origin. Give it a chance.