Harmer's background felt overwraught to me; not bad, exactly, but the kind of thing I'd expect to see in a movie or television drama.
Bingo. Could not have put it better myself. The whole thing felt like a TV episode.
Plus I'm somewhat averse to the whole trope of "tortured soul in hell now works as the devil's errant boy". Maybe it's more exciting to people who grew up in a Christian upbringing and therefore setting a story in Hell has some sort of "forbidden" aura of mystique for them. For me, it just feels silly.
Again, you are right on the money. From a personal standpoint, I found the whole "mean streets" theme coupled with the "blues-devil" Hell pretty lame.
From a larger perspective, the Devil is not really all that scary for one basic reason: he cares about you. Or, at least, he cares about your soul. No matter how bad it looks, there's at least the possibility he's willing to negotiate with you on human terms. Being abducted by Yog-Sothoth who vivisects you no matter how loudly you scream and beg for mercy - now that's terrifying.
From a writing perspective: the word choice, diction and sentence structure were admirable enough. However, I thought it started off vague and slow which instantly turned me off to it.