I won't go into the plot much here, but I'll say this: close-read this one. Don't be surprised if you finish it quickly, only to find yourself missing a thing or two. Read it over a second time, taking it in slowly, and it should all fall into place.
That would be my main criticism, actually: Fegredo doesn't have the same sort of "leading" style that Mignola does, so it can be a challenge to know where the artist wants you to look. That interferes with the flow of the comic a little, and makes the circumstances of the initial conflict a little confusing.
Also, as much as Hellboy hates it, his adversaries usually talk more! The Council of Witches don't explicitly state what their problem is, and Gruagach (Hellboy: The Corpse) is vague as can be about what he's lugging around in that box. It's a little reminiscent of a short-lived Guy Davis project, the noir-superheroic "Nevermen", in that you have to read very closely, and even then, you have to infer some details.
I thoroughly enjoyed the tour through Russian history, though, and Mignola indulges us with a fight scene that, reminiscent of "The Wolves of Saint August" from The Chained Coffin and Other Stories (vol. 3), takes many pages indeed to come to a proper resolution. It's worth it, though: we get a stronger sense of the forces at work, and, as always, we see mythological figures taking themselves way too seriously. A delight!