This is a curiously weightless book. It seems detached from place, from time, and suffers from that detachment. If I spend more time wondering what time period it's taking place in that being engrossed in the story, then there's a problem. Technologies are variable, references are all over the place, and the writing is uneven. But there's a hint here of something better.
It will probably not surprise you if I say that Johannes Cabal is a necromancer. But further to that, he's a necromancer who has sold his soul to the Devil and would now really like it back. The Devil tells him that he can have it back, providing he has 100 other people sign their souls away on the dotted line. And provides him with a carnival with which to do so, travelling from town to town.
(I dunno, one might think urban environments would be more the thing, with the population density and all, but I guess if the Devil gives you a carnival, you have to make...carnivalade?)
Cabal enlists his brother, who may be a vampire, but is also the moral centre of this novel. Horst the vampire is an interesting character, but needs a bit more elaboration to give him more depth. And that is pretty much a refrain I could give to much of the book. Cabal is a complete bastard, so we need the character to root for, but we get much more Cabal than Horst. While Cabal is sometimes amusingly snarky, he also seems a little sketchy, both in what he's doing, and the way he is just sketched in rather than developed. (This seems partly because the author is deadset on withholding information that might have helped me connect with Cabal until the last few pages. One of those cases where the reveal is nowhere near worth what it cost in potential character development over the preceding pages. It also wasn't that good of a reveal - I'd kind of assumed that was what was going on from the first few pages.)
So, when does this take place? The carnival feels late 19th century/early 20th, but perhaps it's anachronistic. But Cabal talks and dresses that way too. Except we have references dropped to Al Capone, Hitler, and LSD. Howard steadfastly refuses to root this in a time, and to a lesser degree, in a place, and that hurts the book. Not knowing when a book takes place is not a good way to go. I don't need to know that it started on July 21, 1890 or 1910 or 1935 or 1972, but more specific would be good.
The same goes for place. I finally decided that I think it takes place in England, but I was never entirely sure, and for the first half of the book, I was waffling between the States, where the carnival, particularly in the form it is described in the book, is more of a thing, and perhaps England. The speech patterns were no help.
As for the story, well, at times I was interested, but never engrossed. There was always this detachment, this sense of the author not committing to place, or time, or event, or character. If you're going to have a main character who, in many ways, is a monster, have a main character who is a monster. If he's going to be genuinely conflicted, have him genuinely conflicted. It is not a good sign that for much of the book, I couldn't tell you how he felt about what he was doing, other than vaguely irritated at the menial task. That itself could work, if it were pursued further.
But some of the writing is good, some of the ideas are interesting. Howard just needs to root his books more, make choices for time, place, and character, and drive for those, instead of drifting between so many options that I start not to care very much.