But historically, it's a notable story for those geeks who care about such things (hi guyz!). This story feels largely like a retread of the first Impostor story with Wilkins the Butler, with the added similarity to Impostor #2 Paul Sloane by giving Blake a background in theatre. At the same time, it's on the cusp of the Silver Age, which means outlandish camp, paper-thin premises, and crack galore. As such, I think Blake's story influenced the actual return of Two-Face, when Dent got rescarred and went on a ridiculous spree right out of the Adam West TV show.
So yeah, this story ain't good. But it's plenty of fun, and the cover is also one of the greatest Two-Face covers of all time. It's also, I might add, a clue.
Scans are from Batman #187.
Tangent: One of these days, I really have to do a proper post about why I strongly prefer Harvey to have brown hair rather than black. Batman: The Animated Series is an exception, because they also made it a point to give Harvey distinct facial features. When he's drawn generically handsome with black hair, there's literally no way to distinguish Harvey from Bruce Wayne.
Anyway, Harvey recounts his whole origin for everyone there.
... Way to go, everybody. Hey, remember that time I snapped and transformed into an insane monster? Let's dress me up exactly like that again! You know, for kids! Also, I like how even Harvey doesn't seem to notice what's kind of glaringly, obviously wrong about that photo of Two-Face.
In my educated opinion, the entire story is worth it for the last panel. Between Blake and Sloane, I'm starting to think that the Impostors have way more fun than the real Two-Face. Not having to deal with angst and torment probably helps. And yeah, sorry for the spoiler, but I imagine that you've already figured out that "Two-Face" there was Blake from the start. Either he's a fantastic actor and makeup artist, or Batman's as dumb as everyone else in this story. How dumb, you ask?
But just having a brilliant disguise to cover up his cunning disguise isn't enough for Blake (who could have, y'know, JUST TAKEN OFF OR CHANGED THE MAKEUP), oh no! There's a second part to his cunning, cunning plan: an inflatable head. Not the whole body, mind you, just the head. But how, you might ask, HOW could he possibly use that to help give Batman and Robin the split?
Behold: George Blake's finest hour of villainy:
BRILLIANT. But only because BATMAN AND ROBIN ARE IDIOTS.
Wait, wait, I gotta go back even further and give one panel special attention:
Batman and Robin, riding a bicycle built for two, chasing after a fake Two-Face in a pushcart downhill. I fucking love comics.
Since I've already gone over my self-imposed page limit, we'll cut straight to the ending. If you'd like to read the whole story, it can be found in the half-great half-terrible trade paperback collection, Batman VS Two-Face. For now, here's the wrap-up, where the Impostor has been apprehended and exposed after Batman discovered Blake's make-up kit:
Yes, the one mistake Dent couldn't have made! Even though he didn't actually notice it any more than Gordon!
... Wait, so if Blake will still be in Two-Face makeup by the time he goes to trial... when the hell WILL the makeup wear off?! Did Batman just create a mirror-image Two-Face with Blake, who's now stuck that way forever? Good god, man!
At least it's still a happy ending for Harvey Dent! Sure, this is the second time he's been framed by someone, but at least he didn't suffer a near-breakdown from self-doubt this time! Still, after three impostors, you get the impression that these writers respected and liked Harvey's happy ending, but they really wanted Two-Face back! I suppose they tired of trying to work around ways to have their cake and eat it too, which is probably how we got the real Two-Face back shortly after this story... only to have him disappear into obscurity for the entire Silver Age.